My compressor squeels like a pig

[71CHEVYSHORTBED402]

It was rebuilt. The compressor worked for maybe 50 miles, it's basically a new 71 truck, running 134A in the system. Took it out today, turned on the AC and the compressor had a PIERCING HIGH PITCH squeal to it. The other day I ran it, started the AC and it smelled like a dead animal. Connection, I don't know, but there aint no dead animals in my system, probably

I noticed the belt was on loose, and with the AC on the compressor pulley fluttered with it. Hmm, how'd that happen. Re-tightened everything. Tension allowed for a 1/4 turn on the belt like I think it's supposed to. Wow, that worked. A whole 20 seconds and the belt's loose again. The belt has 100 miles on it. What the heck? It only squeals when the compressor is on.