Some, most, all???? U-joints, at least mine, have a location where a set screw can be removed and a grease zerk installed. If you suspect its the u-joints why not try and give 'em some love. Crawl under and take a look. Or perhaps you could soak one U-joint at a time with spray lube, take it for a drive and see if you've found the problem. If you must drop the driveshaft, the bad u-joint quickly becomes obvious.

I recently had a drive shaft support bearing that would scream out to me every so often. I bought an 18Ga needle attachment for my grease gun,pierced the bearing shielding and filled it up with grease. Been quiet for 2,000 miles. I'll change it out, but just don't feel like it right now.

--
'90 245 285k, '93 945 296k