Yeah, that's usually a good sign that 1 or both of the u-joints are worn. If you come to find out that one is bad, you might as well do them both. Remember to mark it first, cause it is balanced. Just take a piece of chalk and draw a line across the driveshaft right to the differential housing.
You can tell which one if you get down under there and take the driveshaft in one hand right near the u-joint and grab the transmission yoke on the front or the flange for the rear on back and push and pull with both hands and twist back and forth also. Any movement and they will clang or you can just stick a big screwdriver into the u-joint and move the screwdriver around in case you don't want to get your hands all dirty.
When checking the back, also check the ring and pinion backlash by grabbing the flange and turning that clockwise and counter-clockwise. There should be a little play and maybe a clink but no clunk. Also, move the flange up and down to make sure the nut is tight.
If the seal leaks do that while you have the driveshaft out, same as in the front if the tranny seal is leaking.
When under there also look for any weights that may have flown off the driveshaft although it may be out of balance just because of the u-joints being worn.
Do you know how to replace u-joints? You need a big vise and a big hammer.