Help me diagnose the cause of this high pitch whine

[pwnsweet]

Thanks in advance for reading/helping.


This will be long so I'll get straight to it. My '03 E85 3.0i has a high frequency "whine" sound that presents around 1600-2000rpm (detailed testing info below). I do not exaggerate when I say that it drives me absolutely insane and I will sell the car if I can't find and fix the problem. It's been there since I bought it (9 months ago) and it's the type of high frequency sound that aging people stop being able to hear as the frequency range of sound that their ears can hear begins to narrow.


To put it another way, it sounds exactly like "coil whine" from a computer component under load/stress. Another way to describe it would be the high frequency "static noise" from a speaker that's turned on to full volume but isn't playing any music. Hopefully you now have an idea of the type of sound I'm talking about.


Some observations:
1. Only seems to happen during throttle/acceleration. ie, going from 1600rpm up to 2000rpm. Doesn't happen on the way down (no throttle, 2000rpm down to 1600rpm)
2. Only occurs when car is in gear (no sound when revving in neutral at standstill or moving at 70km/h)
3. Occurs in all gears (including reverse)
4. Very, very slow/light throttle from 1600rpm up to 2000rpm results in the sound being very faint/unnoticeable. In contrast, heavy/full throttle in the same rev range results in the sound being most obvious. This implies the sound "intensity" is related to engine load
5. The sound appears to be coming from the front of the car. This was determined by the fact that the sound is easier to hear when the foam pieces (both) are removed from the sound generator, and harder to hear when the foam is in place. (For the uninformed, the "sound generator" pipes the engine sound into the cabin through a tube. This tube has 2 foam pieces, one at each end of the tube, to dampen the engine noise)


Things I've tried to fix it:
1. The local mechanic thought it was the water pump. He replaced the pump and thermostat but, notably, not the belt or tensioner bearing.
2. I checked the air intake boot and all associated tubing for cracks. A very, very small crack was found and plugged


Details about the car:
1. 85000km
2. Automatic
3. M54B30 engine

[tekoo]

How about turning the A/C on? Does it trigger the sound?
How about turning radio on/off? Does it have any effect?

Also if you have a cellphone charger (or any other device) plugged into your DC outlet try removing it and see if sound disappears!