Vibration under load from 30 -50 mph
I don't know if this is related or not but a week ago I backed out of the garage in Full Time 4X4 and felt a clunk. (Icy driveway when driving into garage and wheels slipped so I engaged 4X4 and forgot to disengage). I switched to 2wd and all was fine as I drove away. Then about 2 hours later, I felt a vibration when between 40&50 mph like I was driving on rumble strips. I took it to a shop and the mechanic test drove & suggested brakes. I took the brakes apart and cleaned them up - all seemed fine and no change - new brakes about 40K ago lots of pad left and rotors look OK. Tires are now about 4 months ago so I don's suspect the balancing is out and all weights seem to still be there. Now when accelerating slightly between 30 & 40 mph I get a real bad rumble strip type vibration. If I let off the gas, the rumble goes away - give it a little gas and the rumble comes back. Feels like it is coming from the right front but it also seems like it could be a vib from the center of the vehicle so I suspect a drive train component. Steering wheel is fine during all this. Coasting downhill has no vibration either and applying the brakes doesn't change anything.
I'm taking it to a local mechanic next week to have a look on a hoist because I'm stumped. To me it could be: bearings, Front CV joints, Drive shaft U joints - hopefully not front diff or anything more serious - how do you diagnose where it is coming from? Any ideas? Safe to drive?