Why is the rear end gear whining again?

[Dino]

I know I have asked this and I have read a ton of posts regarding the subject but I got a bit confused...

Last year I removed the 3:55 gears and installed 2:96 gears.  The 3:55 gears were quiet but the 2:96 have a whine to them.

It only occurs at low rpm and in the 30-40 mph range.  I'm guessing a bit now because I don't have a working speedometer to check so I'll do a trip with the gps this weekend.  The annoying part of this is that it whines at cruising speed.

It's easily heard with windows up or down, but it's not as bad as some I've heard.  Oh and it only whines when I'm on the accelerator, as soon as I let go it stops.  You'll never notice it when you pull onto a road and accelerate, slow or fast, towards 45 or more but it's when cruising, when it's supposed to be quiet so you can enjoy your surroundings that it whines.

It's not something I can't live with but if this is something I can fix then I might as well.  Is this a matter of adjusting or are the gears simply worn?  I think they came out of an old Coronet.

As for the actual whine, we may all have different ideas on this, it does not sound like grinding metal nor does it get better/worse in a turn or anything like that.  Best way I can describe it is like a howling sound.

[Chryco Psycho]

the load side of the gears are not meshing correctly if they were it would be silent

[Dino]

the load side of the gears are not meshing correctly if they were it would be silent

Does that have something to do with the preload setting?  Which btw I only was able to do with your help so once again thank you kind sir.   

[Cooter]

Sounds like a revisit to that preload is in order. Get ready, cause they will whine from now on...My