Did I break it?
To give an example of how it sounds youd have to compair it to a old school rollercoaster going up a steep incline but with an added grinding. I felt it all the way through the shifter. Did I blow the rear end? Is it the rear end? Could it be the tranny?(Tranny is an 02 with under 18k miles)
Rear end noise will be constant, and get worse with increased speed. It will only go away when the car stops. Pressing the clutch in or shifting to neutral and having the noise disappear tells me it's probably not the rear end.
BTW...did you do something "stupid" to suspect the rear diff. (Like a 7K RPM clutch drop....revving to the moon, etc.?) Rear diffs don't normally go bad...unless you beat the hell out of them at the track (ie slicks) or do something really violent with the trans on the street.
But from what I can tell (without jacking it up) it has no gear oil in it. 

