Has anyone had any experience with chainring bolts coming prematurely loose? I've been having that happen more often than expected. Last season I lost 3 bolts on my granny gear, this season I've lost two on a timing crank and three more have come loose on the other timing crank. I usually go over the bike every spring and tighten things up and shoot grease where it needs it, check for frayed cables, etc. But this chainring bolt issue is really curious.