So all of a sudden a few weeks back my '03 X-5 4.4i starts giving me this really weird sounding engine whine (for lack of a better word) during acceleration. Once you get it up to speed and back off the throttle, the whining pretty much goes away but if I blip the throttle I can hear it.

It kind of sounds like one of those tractor pull engines winding up but not loud per se. I'm thinking it's an air leak of some kind coming from either then engine or the exhaust system.

Any thoughts would be greatly appreciated.