It was somewhere in the high 30s this morning, coldest start yet but clear and nice. Something down in the drivetrain started screeching as I pedalled, never heard that before. Then in a few minutes it stopped, presumably after the parts got warmed up. Best guess is it was the bottom bracket, which I have neglected to open and regrease. I've been getting by with a stragegically aimed squirt of WD-40 every few weeks to stop the squeaks, but that may not work much longer.