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what does the noise sound like to you though? it could just be bearings, they make a moaning sound like a wahhh wahh wahhh wahhh wahh...gear noise is typically a speed variable whine....
gears can be had for cheap if you look hard enough, they are normally about $170-$185 a set new, depending on where you look. Installing them-unless you've got an angel sitting on your shoulder, a pinion depth checker, and a dial indicator gear install is a very precise process...better off taking it to a shop.
they should be less than $150 to install though