Noisy rearend 69 barracuda 318 car

My dad bought my dart new in 67. he kept notes of everything that has ever been done even washes and wax. in his notes in the first few hundred miles he noted rear end (7 1/4) noise / whine at fwy speeds same noise loaded or unloaded. The dealer rebuilt the rear and the noise was still there. For the next 20 years I recall hearing the noise and I assumed it was normal. when I inherited my dads car last year I drove it and heard the noise. I did not recall it being that noisy and I assumed after 300,000+ miles the bearings were going. Only after I started collecting parts to swap over to an 8 3/4 did I find his records from when it was new. If I had I might have just left it alone.
Hearing others with the same issue makes me think it is just a design flaw of sorts.