45 m.p.h. whining

You're driving too slow.

Is it coming from the rear end? If so it's your ring & pinion whining. May need to have that differential looked at.... May want to check if it's got any oil in it.....

Stephan

Do something now! Check externally for leaks, a low fluid level will destroy a gear pretty fast. A greasy, messy rear cover is a tell tale of a leak. Have it checked out, mind you when it whines it's already late but might not be to late...

Serge

Take the service writer on a drive with you, and duplicate the problem. Chances are it will be worse AFTER some freeway driving, if it's what I think it is. I had this on my 2000, it's likely the ring & pinion assy. replaced under warranty. The ONLY way they could not use the "can't duplicate problem" bullshit line on me was that I took the service writer with me on a drive.