Originally Posted by
Shimagnolo
In my experience, a chainrings last many times longer than a cassette. Symptom of a worn-out chainring will be "chainsuck" when a new chain is installed. i.e. instead of smoothly leaving the chainring on its return to the RD, it will "stick" to the bottom of the chainring. In a mild case, it makes a rattling noise as the RD tugs it off the chainring. In a severe case it remains stuck to the chainring and gets rammed into the underside of the FD.
This. I'm dealing with this exact situation right now on my primary bike. Probably the easiest ways to tell are: 1) put a new cassette on and see if the problem went away OR 2) have someone watch you from the drive side and look for the chain to ride up the chainring instead of releasing (if you don't have an observer... look down at the RD and see if it "JUMPS" on the skips... that'd be chain suck).