Noisy rearend 69 barracuda 318 car

A rumbling kind of noise would be axle bearings a whine that gets higher in pitch would be in the rear .What kind of noise is it?
A whining noise as you push down on the excellorater and whines when you let off. I took it out on the highway and it seems to quiet down as you cruise. The fluid I took out of the rear today was a brownish color. Of course I don’t have the back seat in the car because I just had the top installed so it may make the rear end even louder
Pat