Does anyone know what this noise could be?

[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.