So what was the problem?
I've had bent yoke, bent drive shaft, bad pinion bearing, bent axle, bad U-joint, misaligned drive shaft, incorrectly installed motor mounts, and engine not dial indicated to the bell housing cause vibration. I've had and have Studebakers that vibrate a little at 35 mph. No reason, they just do but that doesn't pertain to an RQB. My son used to be a Mustang fan but they vibrate - they just do. Ford pick-ups are noted for suddenly going into violent convulsions - they just do (and I don't believe the geniuses in Ford engineering ever figured out why. (It happened to me once and it was really scary! Felt like the whole truck was disintegrating around me. Stopped looked over things and started back out and it was just fine and never did it again.