My 320D has an odd noise, similar to the noise made when rusy discs are clearing off after they have been stood for awhile or almost like a Darth Vader breathing noise. Its an auto, Ive had the gear box checked out with a clean bill of health.
There is no loss of power and fuel usage is normal, its just this noise which only lasts for a few seconds as I ease off the power, Im told that it could be a noisey waste gate on the turbo and BMW told be its too do with having an after market Cat fitted.

If anyone else has heard of this or even has it and has found a solution I would be very intrested to hear. I have a worry that my Turbo will soon give up on me or something equally as depressing.