Just an update in case anyone's curious (and 'cause I hate it when people post stuff, then never follow up) ...
Once my wife got to her destination the clutch noise became intermittent, so she didn't bother to have a mechanic look at it.
From poking around on the net, I discovered that a clutch replacement is an especially labour-intensive job on the Xterra, and generally costs at least US$800-1,000 south of the border (some folks have even paid US$1,500). I thought about getting it replaced down there, but if the job was botched, it would be kind of hard to get any warranty work from 2,000 kms away. Besides, I'm sure my wife didn't want to spend her holiday in a mechanic's waiting room.
My wife's home now, and we had our trusted, local mechanic have a look at the X the other day. He agrees that it's a bad throwout bearing, and told us to expect the new clutch to cost $1,500 to $2,000. Ouch. Worst part is, he told us there's no way that the bearing should have failed so soon. He figures that it was probably installed slightly off-centre at the factory.
Hmm, now that I think about it, we've always had to push the clutch pedal very firmly to the floor in order to engage first gear. Just figured it was a minor quirk, and no big deal. Maybe it was a symptom of an improperly aligned bearing, and we should have had Nissan repair it while we were still under warranty.
