Well, I got a chance to get it up on a rack on Friday...checked the flex disks as suggested and both appeared fine. Could not find any slop or unusual play in either axle, driveshaft, or rear end. Rear end was slightly low on lube, but nothing that would be a cause for alarm (I changed the oil also, as a matter of course - no sign of metal). I had about given up when I noticed that the plastic "sleeve" around the right rear shock had slid down past the shoulder that holds it in place and was laying loose on the bottom control arm. I got to wondering if, at certain angles (like when accelerating) if the axle or CV boot might rub against it, causing it to bounce and make a thud / clunking noise. I put it back in place and shure enough...noise is gone! Funny how something so trivial like that can mimic something more serious. Sure had me stumped for a while, though!