changed gears in a 741 now have a whine

Backlash will cause no whine. The pinion gear depth is incorrect.

It can if there is an excessive amount. I pulled a 3rd member from a guys car to check it for gear whine and it had .038" backlash. Amazingly nothing was ate up from all the slop. I tightened it up and checked the pattern and it looked good so I put it in and it was quiet. That was a rare case of course but you just never know.