[Sunny D]

Hello all, I am in desperate need of some help. Back in July I bought a 2011 E90 with 5800 miles on it. A few months ago, I noticed a very high-pitched noise in the cabin when driving. Here is what I know.

- Was not there when I bought the car
- Only changes has been PPK Stage 1
- Noticed noise at around 9K miles, now at 15k
- Noise only happens when the engine is on
- Noise varies with engine speed
- It is very noticeable, when I first start the car. I can hear it change pitch until the engine settles at idle and then it is a constant noise.
- The noise is VERY soft
- I have not touched anything with the electronics, radio, engine, anything

Brought the car into my dealer:
- They said the confirmed the noise
- Replaced the "radio" and re-coded the radio to the car
- Picked the car up today, and guess what, noise is still there!
- Met with the techs, and naturally NOBODY can hear the noise.
- Dealer does not know what to do, but they are being very helpful and really care. But they do not know where to look.

My assumption is the noise is coming from the stereo, it is almost impossible to tell. Does anybody here have any experience with anything like this? My thoughts are it is a ground loop or a bad amp. I just checked the amp, but, it seems to not be grounded. Anybody know where the ground is so I can check it? Any other grounds I should check?

Any help here would really be appreciated, I fear I will never figure this out and be forced to sell the car. The noise is driving me nuts!