I recently got new FRPP 4.10 gears and an Eaton Detroit Locker Carrier and I drove the car home fine with no noise that I noticed and about 50-60 miles after getting the gears installed I started hearing winning/whirring and it got a little louder and then stayed about the same loudness since. It's only in 4th 5th and 6th. 4th is pretty faint and In 5th it's loudest when I'm just feathering the throttle. the loudest is 6th gear. The installer assured me all the measurements on the gear install were done correctly and that if it was gear noise it would be happening in all gears, not just 4th 5th, and 6th, and that it might be my trans acting up from the new torque. The noise in 6th is really annoying and I can hear it through my exhaust and music on the freeway.

 

Gear whine can vary depending on the loading on the gears, and the speed that the rear axle is turning . . . often they are quiet when under load and/or turning slow, and more whiney when coasting or under light load and or turning faster . . . so I think that is probably what you are hearing. in the higher gears you are generally going faster and there is less torque on the gears, and they whine more. Try coasting at highway speed with the clutch in or in neutral and see how it sounds.

Some people say you should "break in" a new set of gears and some say that does not matter; in any case I guess it is too late for that now.

Also some say they will not whine if installed correctly; and others say they can whine regardless. The steeper gear sets generally seem to whine more. My 3.73's whine a little (it's subjective) and my installer did check the install and says the install is as good as they get . . . you never know, but he has a real good reputation and seems like a straight shooter, so I am inclined to believe him.

But the bit about the trans acting up from the torque is total nonsense -- the rear gears do not change the torque that the transmission is seeing at all. So that does make me question anything that installer is telling you.

If it's real bad, you could ask the installer to check it. Some say the mesh pattern is the bottom line; others say the preload and other stuff matters regardless of the mesh pattern. I think the mesh pattern is the result of everyting else and that's why it is the "bottom line" but I am not sure; maybe someone else will chime in with more specifics.