Rear End gear Whine

I'm going to assume you don't have the dial indicator to check backlash if you don't know where it is. Because the teeth sweep accross each other, a whine can be created by not having the same backlash as you did when you took it apart. My guess is, it's too tight rather than too lose. But you'll have to see. Get a dial indicator. The spec is .007-.010, but a used set may be as much as .012". The trick is to get the reading first, and reproduce it after...