77 f150...open carrier 3.50 stock 31 spline 9" rear end.

I let off the gas and can hear a sort of grinding and/or clanking coming from the back.

On the frwy I let off the gas nearly all the way and it's got a disgustingly sick vibration coming from back there.

On visual inspection the u joints look ok and feel tight by hand movement...though I may just replace them anyhow.

Research tells me possible pinion problems with the rear.

Anyone else have an issue like this? Was it pinion problems in the rear? Should I just check the torque setting on the pinion nut, or is it more than likely that bearing going out? The rear feels very tight and is very quiet while accelerating and cruising,..it just flips out with the foot off the gas.

If it's the pinion bearing, anyone every replace one on their own? what is the level of difficulty? I'm skilled enough to rebuild mustang t5 transmissions and the sort, and have my own press in the garage, so I'm thinking maybe it's something I could have a go at.