How long has it been since the slipper shaft,idler gear, diff gear, spur gear and/or pinion gear have been replaced? I had this same issue with mine, and replaced these parts and now its almost too quiet. If you look at the side profile of the gear, they will look pointy or star like if they are worn, and this will make a lot of noise...My son's SC10 is getting loud right now, and its prob time for replacement of some or all of the above.