I'm struggling to find the source of vibration in the drive system.  Took the feederhouse off this winter for new floor and wear parts, put back on with new belts, but didn't mess with the variable sheaves as everything seamed fine there.  

I've run maybe 130 acres or so now this spring, and for the last day or so it seemed like the feederhouse system has had a rumble/vibration to it.  With the belts loose this morning it seems like all the pulleys are tight and turn smoothly, although I didn't completely remove the lower variable belt.  The threaded tube for upper sheave alignment had broken, so welded it back together and realigned the top, but problem is still there.  The worst of the vibration appears at slow speed/half throttle, or about 350 rpms on the shaft, which really makes the reverser box shake on the rubber mounts.  Going to full throttle, 480 shaft speed, the vibration is way less, but still getting a pretty hard slap on the variable belt between the top idler and reverser.  Is it asking for a lower sheave job, or what am I missing?