Loud whine in rear end on 2006 Ford F-150

Noticed a leak in rear-end seal, had it replaced. it was low on fluid;1000 miles later, hear a loud whine from rear end- sounds like mud grip tires. Noise is constant and getting louder. Is it as bad as I think?

Asked by for the 2006 Ford F-150
It sounds like your rear differential needs some bearing work, possibly even a new gear set. I think the fluid was low enough for a long enough time period that the metal parts were run dry and thus damaged.