Everytime I turn my car on it sounds like it's wheezing or whistling. Everything else on the car has been running fine and I" ve been up to date on any maintenance or replacements. The noise goes away as the car is being driven, but when I slow down or stop it gets louder. It's been doing this for a few months and the mechanic has never mentioned any issues that might be related to the problem. What could be the possibly source of the problem and how should it be remedied?