Allan In NE

1988 K2500 IFS differential, 4:11 ratio.

I've been restoring this old truck, have a "moan" or "humming" type noise in the running gear. Comes in at exactly 42 mph and leaves at 58mph. Sounds like a dry hub bearing seal, but it's not as the truck has been totally rebuilt save the front differential. Front axles "look" okay; no noises when turning whatsoever.

I can lock the front driveshaft from rotating and the noise does not change. 2 wheel or 4 wheel makes no difference at all. Noise sounds like it is right under the seat or perhaps up under the engine area.

Quite a bit of slop (good 1/16") in the left axle stub shaft.

What does a bad axle bearing sound like? Do they "moan"?

Thanks,

Allan