Ah the impetuosity of youth!
I pushed on, sort of - the desert turned out to be way too hot for me, so I re-routed a bit, ended up dong a total of about 1500 miles instead of 2000.
Did a little slow-motion tour of every gas station lot, gave a good listen. The whirring/gear lash noise remained, but didn't get any worse. No new noises developed. This was my weekend of vacation before having to go back to work, so I was being stubborn. And I was rewarded with two solid days of beautiful riding.
It was replaced at about 12,000 mi, we're now at 16,700. Bringing it in today to let them have another whack at it. I wonder if they've seen the service bulletin?
Thanks everyone for the replies. grc probably sealed the risky deal - I'm in my mid-thirties. Still young enough to do stupid chit, *almost* old enough to start listening to reason...