Around 30mph there is a whining noise in my 65 C10. It sounds a lot like the big oversized off-road tires running on the highway. It only starts at 30 mph and stops when I let off the gas. I thought maybe the rear end need more oil, so I brought it to a lube shop to have the oil changed in the engine & rear end. The rear end was bone dry. Well, it now has oil but the noise is still there. It’s weird because it is only noticeable when I press the accelerator. Any thoughts?

Chance

Around 30mph there is a whining noise in my 65 C10. It sounds a lot like the big oversized off-road tires running on the highway. It only starts at 30 mph and stops when I let off the gas. I thought maybe the rear end need more oil, so I brought it to a lube shop to have the oil changed in the engine & rear end. The rear end was bone dry. Well, it now has oil but the noise is still there. It’s weird because it is only noticeable when I press the accelerator. Any thoughts?

Chance

Yep, your rear end was dry for too long. You have wear in your third member.

I suggest either a new ring and pinion or pick up a third member or rear end from a junkyard. Either that or simply put up with it and hope........

RD

It's the EXACT same thing with mine, but mine did have oil in it.
The noise sounds like it was coming from the trans(vibration traveling up the driveline).

The way my Dad & I found it was by putting the rear up on jack stands, in gear with wheels moving, and using a dowl as a stefisscope(sp) (doctors uses it on there patiants ;) ) starting up at the transmission, working are way to the rear end.

It turns out the left outer bearing is wore out, you can wiggle the wheel. It started after taking a 20 mile drive with a small truck load of brick paver stones.
If you're going to be replacing the 3rd member guts, for a piece of mind replace the outer bearings on the axle shafts & seals too.

I'm just going to replace the whole axle with a good used unit.
David