I noticed a whistling noise coming from my turbo and was wondering if anyone had an opinion on what is the cause and if it may be a sign I need a rebuild. At times there is a whistling noise (it kind of sounds like a belt when you first start up a car) that comes from the turbo. It is not constant and sometimes goes away but it definitely sounds like is coming from the turbo. The turbo was rebuilt about 15 years ago and has about 40,000 miles since then. I don't go to the track but just drive the car on sunny days. If anyone has an opinion on what the source of the noise is I would appreciate it. Thanks.