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?