2000 BMW 530 Engine Size unknown Wheel Drive Type unknown Automatic 85,000 miles
My car makes a whistling sound. I hear it when I start to accelerate and it stops when it hits about 2000 rpm and/or 40mph. On the highway (warmed up? High speed?) It seems to stop. I cleaned out the air filter a couple months ago and it appeared to stop, but now it is back. What is this?