Do not 
neglect to re-seal the gearbox with RTV after you’ve got located the proper blend. Even however they are known as “gaskets”, they will not likely seal your gearbox on their own.
If almost everything seems normal, try out altering the gear-mesh. This is accomplished with the mylar “gaskets” that sit between the major gearbox circumstance and the input/output caps. Consider adding or taking away some of these spacers till your gears have approximately one/8″-one/4″ of totally free engage in. Pros can order replacements ($one-2) in various thicknesses, but we recommend the swift and soiled approach of cutting your very own out of a sheet of mylar.
“Groaning”, “creaking”, or “popping” all seem type-of comparable above-the-telephone. The very best factor to do is to disassemble your gearbox and just take a appear at the gears and bearings. The 
situation will normally current by itself in the way of damaged/lacking gear tooth, toasted gears (like that image on our residence webpage), or blown bearings.
My Gearbox is Groaning/Creaking: