At speeds above 55 MPH I feel a buzzing and hear the dome light vibrating. Here is what has been checked.
1. wheels rebalanced
2 off ground testing with weight on rear axle, wheels removed, brake drums removed = rear axle vibration
3.driveshaft u joints checked for movement -ok, - rear of driveshaft at pinion shaft= no runout, at pinion bearing=no play
4. front of driveshaft has little play in transmission output bushing, seal and bushing 1000 miles old- no leak
5 left axle bearing has very little play, right axle bearing a bit more play and a little runout(plus a very slight wobble)
6.right axle shows more c clip wear in-out movement

Summary - the vibration is felt at both ends of the axle housing equally but not as pronounced at pinion bearing end, This is an axle without wheels and brake drums for testing.

Will measure axle shaft at bearing diameter and check for bearing wear surface
Would the driveshaft u joint angles need to be verified?
Is there anything I missed
1986 SS, 90k miles, no accidents, always had vibration since I bought it about 8k miles ago
Thanks, in south eastern Ontario