Whine/humming sound under light throttle, some advise?

[marvgarr68]

my 68 c10 when it still had the 250/th350c whined like this drove you crazy on long trips would change depending on load/speed/rpm it was the trans replaced it never had the noise again. Rear ends makes noise when accel or decel try coasting just barely on the throttle and see what it does if it makes noise then trans is bad

[Rich72C10]

Okay, so I have this too, happens at 40 mph or so. Before that and after it clears up or if I just gas past 40mph. But if the speed limit is like 40hmph it is a bit annoying. The SBC 350 and TH350 was rebuilt and I have likely less than 1,000 miles on. I really don't know what it did before the rebuild, it went out of my hands for said rebuild a few days after I bought it (did not do a lot of joy riding at a steady 40 mph).

I'd call it a harmonic distortion / deep hum.

I have a LWB / two piece drive shaft. Neither it or the differential has been looked at in knows how long.

Did any of you guys find the cause?