My RT is only a month old, after stopping at a stop sign when I took off in 1st gear I experienced a loud knocking noise after shifting to second gear the noise sound got lower and then in third gear the noise went away completely. I brought it to an authorized dealer who informed me that the problem was a rock stuck in the sprocket, which caused damage to the belt and sprocket, also said not under warranty and wanted to charge me 800.00 to repair. has anyone had this problem in the past and is it common? I have not authorized the repair as yet. Please advise Thanks