Rear Whines

I have a 8", Posi, in My 64 Ford, Falcon, Sprint. -- It is a rebuilt rear, has been adjusted 2 times, and it whines, when running, steady, on the level. - It starts to whine around 55 MPH -- it goes away when coasting. -- Opinions, other than "Get a Mopar" -- :D -- ? -- Also, why not below 55 MPH ?
Get her fixed yet?