I guess this has been around for a while, but I just noticed that Gates now sells a new rear sprocket called "Surefit" that features a new design that makes the sprocket fit flush with the Nexus/Alfine hubs. The biggest (and probably only) problem I've had with my carbon belt drive train is a clicking noise that results from the sprocket not interfacing well with my Nexus hub (there seems to be a small bit of play between the two components). I wasted countless hours trying to chase this noise down only to find later that the answer was already on Gates' FAQ page along with a remedy: wrapping teflon tape around the hub-sprocket interface. The tape method seems to work, but I've found that I have to periodically re-wrap the interface with fresh tape to keep it quiet. Looks like they made this new sprocket specifically to address this issue. Has anyone tried one of these yet?