My rear derailleur pulley is slightly, slightly twisted. The last few rides, I have been chain sucking anytime I hammer on the pedals, especially when there is mud in the drivetrain. It only seems to happen when I am in my small front ring though. I replaced the chain, but that didn't help. I checked the front rings for burrs and bends, and they look ok. Is it possible the tweaked pulley is causing this? My next try is to replace the front rings and see if that helps.