Intermitent squeal-ish problem.

I have a 74 Duster with a 225 L6.
Early this weak, I started hearing a weird noise. It's not really a squeak or squeal but similar. It is a intermitent noise. It only happens in drive gear when I'm going 20mph or more. It does not happen while idling. It almost sounds like some kind of fluid leak, but I haven't seen anything dripping. I can hear it through the firewall while driving. It's coming from the driver side of the enging bay, and sounds like its coming from the area where my power steering pump is.

What I have checked and done to try to fix the problem:
Checked all fluid levels, power steering, oil, brake, atf.
checked belts, seem fine, and no noise at idle.
Flushed the heater core.
Fixed a vacuum leak at carburetor.

Anything you suggest could help me out.
Thanks.