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      03-14-2012, 08:49 PM   #13
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Drives: Z4M/. Z3M, E36/46 M3
Join Date: Oct 2008
Location: Teaching the dog to slalom

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Originally Posted by Jax543210 View Post
I took a video of the sound/noise. Doing the actual filming made me analyze how the noise appears all over again. [sadly the audio quality that my smartphone produced wasn't good enough to pick up the noise ]

The noise can not be heard when car is in park and the engine is rev'd, inside or outside of cabin.

The noise is not directly linked to RPM. If I coast at 2-3+ RPM the sound doesn't exist.

However, if I push the accelerator, while RPMs are above 2k, while driving, then the noise appears. I can make the noise come and go as I push and let go of the accelerator above 2k RPM while driving.
After following this thread awhile, and looking at posts that have been added to pre-existing threads on "odd noises", I doubt it's the ECU. I'd bet that's just where the sound is focused, not the source of the sound. Just like rattles, tracking down sound sources is a tough nut to crack.

The noise is there when the engine is under load. This points to it being an air intake related (which includes vacuum parts of the system) or exhaust related: a leak of some kind. If it were some ECU fan or some other fan that would not be present upon acceleration only.

Outside of the brake booster I'm not sure what other systems use vacuum in our cars. But those systems need a check. Then there's the air intake system. Cracks, leaks, etc? Finally, exhaust. Leaks, etc.

The other possibility is that a small demon or gremlin has made a home in your firewall. I hear that's pretty tough to address without a pretty extensive rebuild and a lot of spells. So I really hope it's just a leak. So much easier to deal with than all the all the messy spells and welding.