What is rear diff oil burning up so fast?

My rear diff oil is black and smells almost immediately after changing it to fresh recommended oil.

The previous owner I believe never changed it but I have had it changed twice in the past two days.

both times it was black with only a 30 minute ride.

Also after driving on a dip the howling sound started and has not stopped even after the diff oil changes and a center barring mount change.

pls help