Boo is safely at home now. I'm cautiously optimistic that just the exhaust broke - would explain the air leak (not idling down) and, of course, the loudness. I already have another exhaust, so it may be time to put it back on.
Unfortunately the smallie is out of commission for a couple of weeks. We're out of town this weekend for a wedding, and then Aaron is out of town for training next week. Oh well - at least I have two other bikes to ride!