I had an early used Karmen pulley for a couple weeks. I noticed when I would start the car up it would make noise for a few minutes and then quiet down. When datalogging I noticed it would stop making boost at a point on the graph and fall off. After a lot of head scratching I determined it was pulley slip causing the noise and boost issues. In my case, there wasn't enough friction between the pulley plate and clutch.

The heat buildup on the plate makes sense based on the clutch-to-plate slip I observed.