You hear it at idle? It increases as a function of RPM and not speed? Usually the first suspect of a whine is the rear differential, especially if you only hear it at highway speed.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth