Today's Fun with Boxsters
 

Had a car come in today at 4.30PM with a sheared off belt pully pulley. The owner said he heard something fall off the car, and then heard a bunch of shrieking, and then continued driving the car to the shop. He handed us the part, which happened to be a brand new pulley we installed several weeks ago when we had his motor out for a head gasket repair. First thought was that some accessory had seized causing the the pulley to break free. Nope, everything was perfectly fine. Closer examination revealed that the mounting boss had been cracked for some time, and had finally sheared free today. We machined the pulley down in the lathe so that it would fit in it's new mounting location and fabricated a new bracket to hold the pulley, and off he went at nearly 7PM.

Pics attached.

I've seen this as well.. It featured a bearing failure with the idler pulley and caused the issue.