The picture describes this issue better than I can. What is happening is that in the highest gear (i.e., in the smallest cog) the derailleur folds up as there is more chain to take up. However the lower part of the derailleur is running into the plastic cable guide. Its a little tough to tell in the image but is almost snaps over the plastic part, definitely causing some damage. Any ideas on how to stop this from happening?
SRAM derailleurs do that when the chain is too long or sometimes when it's been sized correctly for chain growth, but looks long with no weight on the bike. Presuming it's a full squish, you can get on and see whether sag is enough to keep it from happening. You could also just go through and confirm the length is right manually. (If it's not a full suspension bike and it can contact the cable guide like that, the chain is too long.)
