Don’t neglect to re-seal the gearbox with RTV after you’ve got found the appropriate combination. Even however they’re called “gaskets”, they will not seal your gearbox on their own.
If everything seems regular, attempt changing the gear-mesh. This is completed with the mylar “gaskets” that sit in between the major gearbox circumstance and the input/output caps. Try out adding or taking away some of these spacers right up until your gears have roughly 1/eight”-1/four” of free engage in. Experts can get replacements ($1-two) in varying thicknesses, but we recommend the fast and dirty approach of chopping your possess out of a sheet of mylar.
“Groaning”, “creaking”, or “popping” all seem type-of related more than-the-telephone. The best issue to do is to 
disassemble your gearbox and take a look at the gears and bearings. The situation will usually present itself in the way of damage
d/lacking equipment teeth, toasted gears (like that photograph on our residence page), or blown bearings.
My Gearbox is Groaning/Creaking: