Hi, this is the first time I've ever joined or posted to a forum so please forgive any lapse in forum etiquette. That being said here's my issue and I need help:

I have an 04 dodge 1500 crew cab 2wd st with the hemi. It was my brothers truck and he'd had the water pump changed sometime before I got it from him. It was leaking and when it started screaming I changed it, brand new Murray pump from oreillys, started it and almost as it was finished burping the coolant it started screaming as well. Took the fan clutch off and verified it wasn't that. Immediately put on a duralast pump from autozone. Same thing it started screaming right as the thermostat opened up. These were both brand new parts, not remans so I'm at a loss for what to do as is our mechanic. For context I work at a mechanic shop and the lead mechanic watched do all the work. Please help.

 

Are you sure it was the pump screaming, and not one of the other pulleys?

 

Highly unlikely to hear the same sound coming from two brand new WPs. Spray some water on the belt while running to see if the issue is the belt itself. Take off the belt and turn everything by hand. Everything should be silky smooth, nothing chalky. While the belt is off, start the engine very briefly. If you hear the sound, it's nothing in the belt path.
How about a video of the "screaming?"

 

Maybe be a weak tensioner too.....

 

True. A weak tensioner could cause the belt to slip. If he sprays water on the belt and the noise quits, I would suspect tensioner or pulleys freezing up.