These are all great suggestions. Not to hijack the thread, but we too are having a similar issue where one of the TB mini gearboxes is louder and not as smooth spinning as the other. The really odd part is that it is worse when driven in one direction versus the other and seems to bind/catch. We've reassembled it many times, reversed the cims, and swapped out internals. We are beginning to wonder if the molded plastic housing is the problem. We are running a
13 tooth cim gear with 14 tooth center spacing.
Thanks for any help in advance.
Nate