Does anyone know what this noise could be?

[Infernous428]

Hi guys, I drive a 2001 boxster, and my car has started making this weird screeching type sound that comes on and stays on after about 5 minutes of driving. It sounds like it's coming from the back right of the car, or maybe underneath the car from the rear right catalyst. I'm not exactly sure what it is, but the car drives fine and there are no dash lights but the noise is completely unsettling. I thought it might have been the AOS screeching, so I replaced it with a new OEM part but it hasn't gone away. Any advice is appreciated.

Video linked below for reference to listen:

https://www.reddit.com/r/Porsche/comments/xaas9b/strange_screechy_sound_from_my_986_boxster_does/?utm_medium=android_app&utm_source=share

[Gigi]

I would put the car on a car lift to have access under the car. Take all under car covers off and start the car. Inspect the area the noise is coming from. You can not find where the noise is coming from the ground. Period. Good luck. p.s. aos does not makes any noise, but white smoke.

[blue62]

Sounds like a fan belt tensioner bearing going out.
But it is a video so it is a wild ass guess at best.

you could remove the engine cover behind the seats and have a listen.
Use a piece of hose (like garden hose or heater hose) like a stethoscope.
That way you can pin the noise down better then just listening in the normal way.

You could remove the fanbelt and run the engine for just a few minutes to see if the noise stops.
if it does then the fan belt tensioner or the altenator or the water pump is the issue.

Keep us posted.

how many miles on it??

[78F350]

Originally Posted by blue62

... you could remove the engine cover behind the seats and have a listen.
Use a piece of hose (like garden hose or heater hose) like a stethoscope.
That way you can pin the noise down better then just listening in the normal way.

You could remove the fanbelt and run the engine for just a few minutes to see if the noise stops.
if it does then the fan belt tensioner or the altenator or the water pump is the issue.
...

I can't get the video to play, but I agree This is the best advice so far.

No harm in replacing the AOS preemptively whether it was the problem or not

Since the video didn't work for me, extra questions:

• Is it only driving the car or just engine running?
• Noises up front could easily be a bearing on an idler pulley or belt driven accessory.
• Two fans on the right side - engine compartment cooling and SAI Blower.
• Loose spark plugs chirp.
• Wheel bearings or brake related noises when the car is moving? I had an E-Brake pad drag that made a whine.
• I'd expect that vacuum leak large enough to make much noise should be large enough to trigger a check engine light.
• Exhaust leak at the header/O2 sensor?

[blue62]

Originally Posted by 78F350

I can't get the video to play, but I agree This is the best advice so far.

No harm in replacing the AOS preemptively whether it was the problem or not

Since the video didn't work for me, extra questions:

• Is it only driving the car or just engine running?
• Noises up front could easily be a bearing on an idler pulley or belt driven accessory.
• Two fans on the right side - engine compartment cooling and SAI Blower.
• Loose spark plugs chirp.
• Wheel bearings or brake related noises when the car is moving? I had an E-Brake pad drag that made a whine.
• I'd expect that vacuum leak large enough to make much noise should be large enough to trigger a check engine light.
• Exhaust leak at the header/O2 sensor?

The video is with the car stationary so that narrows down the issue considerably.

If it was a vacuum leak big enough to hear when standing next to the car it would not only trigger a check engine light as you mention but the car would shake like hell at idle, Although I doubt it would idle with a vacuum leak that big.

I think the SAI blower only kicks in on cold start and for very short time. So I don't think it is that.

If he had an exhaust leak big enough to be heard it should trigger a lean code and or a Cat efficeincy code.

So diagnostics are narrowed down greatly.
the most likely issue is one of the three things I mentioned.
or the engine bay cooling fan as you mention.

In the video it sounds like a "rotational mass squeak" to me.
But it is a 12 second video at idle only so there's that.

If he would have run the video longer and varied engine speed just a little I could have listened for if and how the sound changed.
That can be telling at times.

If he removes the fan belt and runs the engine for a few minutes he can either eliminate three possible suspects (if the sound is still there) or narrow the issue to one of three suspects (if the sound is gone).

So it would be a good diagnostic gain for the time spent.

Woops
four suspects I forgot about the air-conditioner pump.

[Infernous428]

Here is a longer video with more revs etc.. had a smoke test done and there's no leaks found. No engine codes either. Sound seems to be coming around the cats etc. Not sure where what it could be. Mechanic said he doesn't just want to start waiting for random parts replacement and to come back when a code comes up so he knows where to begin:

https://www.veed.io/view/abeb01ba-874d-4109-a15f-58720e9a1c9a

Originally Posted by blue62

The video is with the car stationary so that narrows down the issue considerably.

If it was a vacuum leak big enough to hear when standing next to the car it would not only trigger a check engine light as you mention but the car would shake like hell at idle, Although I doubt it would idle with a vacuum leak that big.

I think the SAI blower only kicks in on cold start and for very short time. So I don't think it is that.

If he had an exhaust leak big enough to be heard it should trigger a lean code and or a Cat efficeincy code.

So diagnostics are narrowed down greatly.
the most likely issue is one of the three things I mentioned.
or the engine bay cooling fan as you mention.

In the video it sounds like a "rotational mass squeak" to me.
But it is a 12 second video at idle only so there's that.

If he would have run the video longer and varied engine speed just a little I could have listened for if and how the sound changed.
That can be telling at times.

If he removes the fan belt and runs the engine for a few minutes he can either eliminate three possible suspects (if the sound is still there) or narrow the issue to one of three suspects (if the sound is gone).

So it would be a good diagnostic gain for the time spent.

Woops
four suspects I forgot about the air-conditioner pump.

[Smallblock454]

I would say water pump.

[Starter986]

My advice is to diagnose problems BEFORE you start throwing money at it. That can get expensive, and frustrating, real quick.

[Stl-986]

AOS wont make any noise.

I suggest taking it to a mechanic

[JFP in PA]

Originally Posted by Stl-986

AOS wont make any noise.

I suggest taking it to a mechanic

Actually, the can and do occasionally make pretty noticeable whistling or screeching sounds when the main diaphragm tears.

[blue62]

Some things I forgot to add.

After you do the belt off test...before you replace the belt spin the idler pulley with your fingers.
See if it turns smooth... or if it has any play front to rear. Do the same with everything you can that the belt turns.
Alternator...air conditioner pump what ever you can reach and turn.
If the noise is gone with the belt off you may be able to "feel" the problem by turning..spinning the pully's

Also is it a standard transmission???
or an automatic (tiptronic)????
If it is a standard transmission get the noise going.
then while sitting still in neutral push the clutch in an hold it in.
Then push it in and let it out a few times.
Does the sound change when doing this????

[Infernous428]

It's a 6spd manual. Sound does not go away with the clutch in/out.

Something else to add, I had the water pump and thermo replaced before.. I dont think that would be the cause.

The car has a jumpy idle currently. And the sound doesn't seem to be coming from the belt area. Seems more like below the car/exhaust area a si showed in the video.

When I have some time this weekend I will try to work on the car and try to run without the belt..

Originally Posted by blue62

Some things I forgot to add.

After you do the belt off test...before you replace the belt spin the idler pulley with your fingers.
See if it turns smooth... or if it has any play front to rear. Do the same with everything you can that the belt turns.
Alternator...air conditioner pump what ever you can reach and turn.
If the noise is gone with the belt off you may be able to "feel" the problem by turning..spinning the pully's

Also is it a standard transmission???
or an automatic (tiptronic)????
If it is a standard transmission get the noise going.
then while sitting still in neutral push the clutch in an hold it in.
Then push it in and let it out a few times.
Does the sound change when doing this????

[blue62]

Originally Posted by Infernous428

It's a 6spd manual. Sound does not go away with the clutch in/out.

Something else to add, I had the water pump and thermo replaced before.. I dont think that would be the cause.

The car has a jumpy idle currently. And the sound doesn't seem to be coming from the belt area. Seems more like below the car/exhaust area a si showed in the video.

When I have some time this weekend I will try to work on the car and try to run without the belt..

Another thing that is easy to check is your spark plugs.
you could have a loose one so check those out.
Just make sure they are not loose don't "over tighten" them.
I am starting to lean toward an exhaust issue.
a leak or a clogged damaged cat. converter.
You could take it to a muffler shop have them put it on their hoist and do an exhaust system inspection. If it is leaking they should be able to tell you.

Another possibility is the engine bay fan it can be triggered (run) with an OBDII scanner that has a Porsche program. like a Durametric scanner.

[Infernous428]

I know it's not the spark plugs. I've had the spark plug chirp before, and it came with misfires. Had all 6 coils, plugs and tubes replaced less than a year ago.

I've connected the car to a Porsche scanner and its so weird it no codes come up.

The majority of the sound is coming from the exhaust area, and I think it might be a leak in the exhaust system somewhere. That could cause a jumpy idle and the suctiony sound.

I will take it to a muffler shop to check for a leak..

Thanks!

Originally Posted by blue62

Another thing that is easy to check is your spark plugs.
you could have a loose one so check those out.
Just make sure they are not loose don't "over tighten" them.
I am starting to lean toward an exhaust issue.
a leak or a clogged damaged cat. converter.
You could take it to a muffler shop have them put it on their hoist and do an exhaust system inspection. If it is leaking they should be able to tell you.

Another possibility is the engine bay fan it can be triggered (run) with an OBDII scanner that has a Porsche program. like a Durametric scanner.

[blue62]

Originally Posted by Infernous428

I know it's not the spark plugs. I've had the spark plug chirp before, and it came with misfires. Had all 6 coils, plugs and tubes replaced less than a year ago.

I've connected the car to a Porsche scanner and its so weird it no codes come up.

The majority of the sound is coming from the exhaust area, and I think it might be a leak in the exhaust system somewhere. That could cause a jumpy idle and the suctiony sound.

I will take it to a muffler shop to check for a leak..

Thanks!

Keep us posted I am always curious as to results.
Good luck with it.