Does anyone know what this noise could be?
 

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

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.

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??

I would say water pump.

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

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.

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.

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

If "you" want to diagnose the cause then you need to start eliminating possibilities.
The easiest way to start doing that is to remove the fan belt (serpentine belt).
If the noise persists after removing the fan belt and running the engine then you will know it is not anything driven by the belt.

If the noise is gone after removing the belt then it is something driven by the belt.

Your not going to get far by just posting video's and asking random people or random mechanics their opinions.
Diagnostics has to be done, that basically boils down to a process of elimination.

I notice a lot of liquid dripping from under the car.
Whats going on there.???

What modifications have you done to the car?
Doesn't look like stock exhaust or it isn't bolted up correctly.

To me it sounds quite like this:
https://www.youtube.com/watch?v=YK2ihM9-JaQ&t=4s

But seriously, you don`t even need to pull the belt, you can just loosen it up by releasing the tensioner roller for a couple seconds while idling using a breaker bar. Everything that the belt drives will stop and that will narrow down the potential causes, as Blue suggested.

It used the have an aftermarket exhaust, and I recently had the stock exhaust reinstalled and that's how they did.

The dripping is because it had been pouring outside and I had just driven the car in heavy rain.

I will start with the belt and see what I can find. Honestly the noise doesn't start until about 10 min of driving. How long can I run the car on jdle the car without the belt?

Drive it 10 min (or whatever) until you hear the noise. Shut the car down for a couple min. Re-start. Is the sound back immediately? If so, you should be able to test it. I don't think having the belt off is a problem until it's been long enough to start overheating (you're disconnecting the water pump). That should take a few minutes I would think.

I've driven around (briefly...it gets incredibly warm when you do this!) with the carpeting and cover plate off. Just make sure there's no loose clothing, etc, that could get caught in the belt/pulley system! You'll get some idea if it's one of the pulleys doing this even before removing the belt. And it'll be easier/quicker to remove the belt.

That would make me nervous—muxing around with that with the engine running! Even just at idle. You're braver than me!

That`s the first thing I do usually to tackle a noise like this and the belt never ran off when I let the tensioner go back to it`s position. But you are right, it`s literally for saving 5-10 mins, as that`s what it takes to remove the belt and put it back on :) So it`s better go safe and take it off completely. It also allows for inspecting the pulleys and idlers individually for play or noise, perhaps it`s just a bearing that went out.

Ok I get the sense that you haven't done much mechanical work or diagnostics on cars.
So I will try to help you the best I can.

Very first thing ......get familiar with what your going to do.

So pull the cover behind the seats and have a good look at the fan belt.
Look at how it is routed...look at how you would remove it.
get all the tools you would need to remove it.
Maybe even remove it and put it back on so you know whats what.

So now you know whats what.

With the cover behind the seats still off take the car for a spin and get the noise going.
Then pull into your work space ...remove the belt and run the car for a few minutes.....3-4....

Use your senses you should if know your car is getting hot long before it gets too hot.
They begin to run different..some sound different...or you can smell that it is hot.. or you may see something that says it is hot.

If you follow and do what I suggest it should only take you a very short time... 2-3 to remove the belt and restart the car.
Things are not going to change much in 2-3 minute of engine off time.
Lets see what you find and go from there.


How soon after replacing the exhaust did this issue start.???

Your exhaust does not look properly mounted from what little I can see.
It doesn't sound right to me either....but it is a video.

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????

Great video
I think it hits some of the sounds:D

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..