rear end hums while on freeway or once it's in overdrive

I am always checking the fluid and I have changed gear oil twice since I have owned it

216,000

It is possible it's just worn ring & pinion gears. Mechanic can tell by rear yoke lash. Have it checked out by a qualified mech. May be some additives that will help. Sawdust isn't a good option, if you have ever heard of such a thing. That goes way back! You could just turn up the stereo....Seriously though, check into the additive thing, Lucus oil stabilizer maybe. You stated you have driven it 80k like this, must not be a bunch wrong with it that's why i say worn gears! One more thing, have ALL differential mounting related bushings checked!

No I would never try saw dust and I do just turn the stereo up I just thought I would see if anyone had the same prob or advice I will try a additive and go from there thanks

It was a joke! Lot of vehicles have this same problem with that mileage. Same advice. Have a mechanic check it out!

I have asked a few shops and they just shake there head and tell me to change the gear oil

could go as high as 2000.00 and as low as 1500 depending on damage