My car has been in the shop for a week and they are just getting around to it! The problem is a sound coming from the engine bay. I believe it is to the right where the turbo is located. I apologize but some of this is a repeat post. In response to the noise described below, the dealer is replacing the bypass valve. Is the below symptamatic of a faulty bypass valve?

1. If I rev the engine to 3000+ rpm's (in neutral) everything sounds fine.

2. When I start to drive and accelerate, a whirring noise occurs. It is not the usual turbo spooling up. It is more pronounced like a "weed-eater/trimmer" would make. (At first I thought it could just be from the belts) It does seem to be coming from the front right side of the engine bay.

3. It is independent of what the RPM's are.

4. It happens with increasing intensity when turbo boost rises from 0 to 7 PSI.

5. After the boost decreases, even though the RPM's remain unchanged, the noise decreases and ultimately disappears once the boost is in vacuum state (0 to -21).

6. Happens for about the first 2-3 minutes of driving (which seems to be about 20 cycles of the turbo spooling up.)

7. After that initial few minutes of driving the problem seems to disappear. If it is still making that noise, it is too quiet for me to hear it.

8. It happens regardless of the outside temperature or how long I warm up the car.

It does sound like it could be a valve located somewhere on the boost side of things. A bpv at least sounds like an easy place to start, since it's a cheap item that's easy to replace.

The fact that it goes away after spooling up the turbo for a while makes me think it's a heat related issue... well, a cold related issue, you could say. When you are idling, you really aren't spinning the turbo or pumping any hot air or boost past the bpv. So even if you sit there and idle for 10 minutes you probably won't heat up the bpv much. But once you start driving and putting some hot pressurized air on the bpv, that would warm it up.

If it is indeed the bpv, I'm thinking it could be the rubber diaphram. Maybe it's got a small leak in it, and when it's cold the rubber in the diaphram is slightly shrunken, so air flows past it making it vibrate. Once it heats up it could seal itself enough so you don't hear it, or it's not a problem. Or something along those lines. :)

Did you or have you removed your Air-box?
If, Yes. It most likely the Air injection Pump.