Bill, you must have BigShots. They seem to be the worst for clampbusting. You have to tighten them enough to keep the shields from rattling, but not enough to break when they heat up. Lots of folks have had it happen to them. I don't know if it's because the V&H pipes expand more than everyone else's or if they use inferior clamps, but it's not a rare occurence.
Since it's never happened to me, I can only offer a suggestion: Get some new clamps. Get everything up to operating temperature. Put on your asbestos gloves and Nomex coveralls. Snug 'em down good while they're hot. Not sure if that's even feasible with your pipes, but I'll drink a couple of Weidbuzzers for you if you think it'll help. Or if I think it'll help. Or if anyone thinks it'll help. Let me know if I drank in vain.