I remember driving the D2 and always hearing a faint humming.

Was driving me crazy.

I even tried to loosen the power steering belt to see if the noise went away..

Thinking it may have been transmission.

But in the video I did get less noise by taking tension off of the driven components like power steering, Alternator and water pump.

That stuff makes a lot of noise!

 

I'm honestly planning on removing my power steering all together. I ran without it for a couple weeks while I was waiting on the parts to rebuild the pump. Honestly with most of the fluid removed from the steering box it wasn't even bad, and I'm pretty sure there was a significant gas mileage increase. Mines still whining even after rebuilding.

 

It sounds like you have ancilliary equipment bearings making an awful noise, try removing the serpentine belt totally then run the engine for a couple of minutes maximum. Also test each piece of equipment by turning it manually and try identify what is making the noise.