Maybe too tight? I wonder if something flexes at load.
Serpentine belts tighten on one side at RPM. That is why they should really be designed with a true tensioner. I had a buddy that put one on his 350 Chevy back in the early 90's without a tensioner and it bent his water pump first time he hit close to 7,000 rpm.
How is the back of the AC compressor held in place?