Whine/humming sound under light throttle, some advise?

[Leviticus]

My 1972 C10 with 350/TH350 is making an intermittent whining humming sound when cruising at around 25-30 mph and under very light throttle, like just keeping it running at that speed/rpm.

Its a weird sound, can't quite trace it down yet, almost sounds like the rear end, but it disappears the second you let off the throttle, which doesn't me its not the rear end. But it seems like it would make more noise under more load if it was the RE.

Anyone have any ideas before I start ripping into this thing? I am hoping its not a trans pump/torque converter, never slips and shifts good.

I am going to be replacing or repairing the PS pump, the whole assembly has some wobble to it at idle, just saw it tonight, almost s#%$ my pants when I saw it.

Thanks guys!