Cold Start Power Steering Chirp Under Load

I'm having an issue with my power steering system making a distinct chirping noise under load, only when I start the truck up cold. The noise only occurs under a 'heavy' load, i.e. turning wheels sharply while not moving, and only does it for the first 10-15 seconds of driving/using the steering. It's worse the colder it is in the morning. The chirp also has a resultant vibration which I can feel thru the steering wheel, as if the power steering is losing partial power and then regaining it cyclically.

Some background on the service of the power steering system:
1995 3.4L V6, currently has 131k, I replaced the steering rack about 20k miles ago with new OEM rack, partially due to a fluid leak on the inlet/outlet hard lines of the rack. I filled with fresh dex atf fluid, and did the lock to lock method to get all the air out. Fluid level is fine and unchanging, although smells slightly burnt. Checked belt tension last week, but don't believe its the belt or the pulley because the issue only happens while cold and goes away permanently after 15 seconds max. I should add that I didn't have this issue prior to installing the rack, and its been happening pretty consistently since then. My thought is that its possible the leak from the previous rack allowed contamination into the system, and messed up something internally with the pump.

Am I incorrect in thinking that the pump has to be the source of the issue? I hate being a parts-thrower instead of doing a full diagnosis, but process of elimination has led me here.

 

Did you ever figure this out?