I lean away from the driveshaft but it you think it is out of balance, here is a trick you can try. It will take some time and you may get tired of crawling under to do it, but it can work. Get a large radiator hose clamp and put it on the driveshaft. Mark where you put it (where the screw part goes) with some chalk or grease stick and start by putting the clamp around 6 inches back from where it connects with the differential. The large part of it will act as a weight. You may have to use 2 or 3 if the shaft is really out of balance, but I'd start with one. Then go drive it and see what happens. If it is worse or no improvement, rotate it about 30 or so degrees (does not have to be exact), make another mark and try that. Keep going until you see if anything changes until you work all the way around your "circle." Then move forward 6 inches and repeat. Like I said, painfully slow work. If you find a spot where the vibration goes away, tighten the clamp well, paint it black and leave it in place.
