Never forget to re-seal the gearbox with RTV following you have identified the proper mix. Even even though they’re known as “gaskets”, they will not seal your gearbox on their own.
If every thing seems to be normal, try modifying the gear-mesh. This is completed with the mylar “gaskets” that sit between the primary gearbox scenario and the input/output caps. Try out introducing or getting rid of some of these spacers till your gears have approximately one/8″-one/four” of free 
of charge play. Experts can buy replacements ($one-two) in varying thicknesses, but we recommend the quick and dirty technique of chopping your own out of a sheet of mylar.
“Groaning”, “creaking”, or “popping” all seem sort-of comparable in excess of-the-cellphone. The very best point to do is to disassemble your gearbox and just take a search at the gears and bearings. The concern will generally present by itself in the way of broken/missing equipment teeth, toasted gears 
(like that picture on our home web page), or blown bearings.
My Gearbox is Groaning/Creaking: