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

[racerbruce]

Greetings to Down Under from Seattle

Air intake related?
Suction around the airbox, filter, mass air flow meter, throttle bodies?
It's happening at a lower RPM
Could it be a vacuum leak?
Sound does not manifest when out of gear (neutral)....
This (perhaps) does not eliminate the drive train (clutch, transmission, drive shaft, differential, etc)?
Any potential for this emanating from a sheet metal heat shield, loose sway bar bolt?

[GuidoK]

I think you should look at the vacuum system, if the whine is really correlated to the load of the engine.
You say you have plugged the intake boot?
Normally you replace them (there are 2; an upper and lower one).
You can also take a look at the rear of the intake manifold (so at the side of the bulkhead).
I think there are a few rubber plugs there that plug off some holes. They can also leak when the rubber ages.

#3, #15 and #17



And the connection between inlet manifold and ICV can leak too.

If you want to look in a more mechanical direction, get a mechanic that has an engine stethoscope ($2 tool....). Listening is the way to look for worn bearings etc.