Noticed some changes in engine vibration in the 1800-1900 rpm range that change with amplitude day to day. Today it is running exceptionally smooth so I decided to check the drive-line alignment. I dropped plumb bobs off three points in the drive train to check total alignment. I dropped one bob forward of the front crank pulley, the next at the forward end of the drive shaft and the third at the rear of the drive shaft. When I sight along the three lines the middle line at the forward end of the drive shaft is about 1/2" off of perfect alignment. My question is, does this make any difference in drive line vibrations being out on horizontal alignment? The vertical alignment is good. I occasionally feel something like a lifting mount somewhere if I let the clutch out too rapidly. Sometimes after some hard and heavy loaded runs the vibrations are more pronounced and then go away after several days of running unloaded. I don't see any evidence of a torn mount or loose bolt. Any ideas here?