My '02 C5 2.7t needed a timing belt and water pump, and when I looked around and decided it was worth fixing, I had the boutique Audi mechanic put in a chip (forgot to ask which).

The effect was pretty obvious, but along with the speed increase there's also a new sound. I'd describe it as a "wishhh-ing" sound, not unlike what a compressed air can sounds like, though not /quite/ so high pitched.

I hear it when I punch the gas and the revs are around 2K. It continues past 3K and by 4 or 5 it either goes away or it gets quiet enough that I can't hear it over the engine.

Then, maybe 10 minutes after I start driving, it stops. I'm not sure if it's in my head, but it feels like the car looses power when it looses the sound.

I managed to catch it disappearing mid-acceleration just now, around 2.7k rpm, and it felt like the car lost some acceleration at a point where it should have been steadily and rapidly gaining. I'm not 100% sure that I felt the acceleration drop, but I'm about 87% certain.

It only makes the noise when I give it a lot of gas, not necessarily floored, but close. Also, I must be in gear. In neutral or with the clutched depressed I can't hear it at all.

It seems to be on the driver's (left) side.

​​​​​​In addition, the new water pump seems louder than the old one. When the latter failed the car sounded like a jet engine or a bathroom hand dryer, and it got louder with rpm. Maybe now I just hear it where before I didn't. I'm inclined to think it's not related to the other sound, assuming it really is louder than before, but I thought it worth mentioning.

Thanks in advance.