pinion bearing would make noise under acceleration or deceleration and may quiet down at cruise. Get under there and jerk on the drive shaft back there and see if there is any play at the yoke. 7.25 takes grease at the bearings, not shared with gear oil. Not sure with the 8.25. 8.25 is perfect oval, 7.25 is sort of hex shaped.
It has to be an 8.25 because it is oval shaped I did change the the pinion seal because it was leaking. Do you know if the bearings get greased from the rear end fluid?
Pat