Just picked up an 05 S type 4.2 with 71k miles. Drives great but while driving home on interstate 60 to 75 mph, notice every time I touch the throttle I get a whine which subsides immediately upon release of throttle. Sounds like rear of car right side, but could be middle right side. Weather was hot and dry, 90ish. Does it with manual throttle and cruise control.

 

Suspect a wheel bearing.

 

A wheel bearing will make the same sound regardless of throttle- do you hear it in neutral? More likely its the diff - this will wine under drive & stop or at least change with neutral throttle setting.