Ok, so I think my U2A is shot after all - a replacement cable didn't do the trick since I'm still getting those pops from 'tabling' like I did below. So I opened it up and of course didn't see anything, but I'm getting a tiny rattle when I shake it that I can isolate to the coax input jack. I assume this is a Bad Thing (tm) but I thought I'd check to see if anyone else has the same rattle on a working U2A - maybe it's the nature of the coax connection or something.
If anyone's got a U2A or a U24 they wouldn't mind loaning out for a week or so I'd love to test it and make sure before I drop a couple hundred on a new card. Despite appearances, I really do take good care of my gear...I haven't dropped this thing for days now.
--Dave