rear diff clicking on deceleration 02 wrx

I am stumped on this...02 wrx manual. I am getting a loud speed sensentive (faster clicks as speed increases) click coming from the rear differential. I pulled the driveshaft off, the ujoints feel a little sticky, but nothing that would cause a loud click. the sound completely goes away when any amount of throttle is applied and the tranny is in gear. but on deceleration, the tone of the click changes slightly when engaging and disengaging the clutch. There is play in the differential when moving the pinion back and forth by hand...but I have no idea how much is allowable. tia
-Dustin

 

Pull the drain plug and check for metal deposits and gear teeth

 

Yea, I should have added, thats the first thing I checked...fluid was clear and full, I only got 2-3 small (like 2mm long of the finest lead from a mechanical pencil) pieces, other than that, even put a small magnet inside and thats all that came out.

 

What are u runnin for fluid when was it last changed.

 

I have no idea on the fluid, the rear bolts look like they have never been taken off til now. So I assume the original was in there. The car has 103k on it. I have the drive shaft off and turning the pinion by hand as fast as possible, I can mimic the sound that its making...I am betting now that its one of the front pinion bearings making the gear mesh incorrect.