My 1998 M3, with automatic trans, recently started making a whirring sound when driving. No noise when at a stop, but starts making the noise as I accelerate. Whirring gets higher in pitch as I go faster. Does not sound like a wheel issue, as it sounds like the whirring is moving much faster (rpms) than the wheels. In neutral, when the engine is revved, there is no noise. Car must be moving. Anyone?
Wheel bearings? Worn gear or bearing somewhere in the drive line? Someone put playing cards on your spokes... (ok... I'm being a smart-***) You need to narrow down a bit where it is originating from. If is is strictly speed related then it needs to be in the drive line between the output shaft of the transmission and the wheels. Chuck
From experience if it is a bad wheel bearing, the noise should change (or even go away when turning left or right).
Rear diff? I've heard speed-dependent whirring from rear limited-slip differentials (LSD) before. Pinion bearings. But only if the sound doesn't change depending on whether you're turning like @M3Driver wrote...
