Just watched the video...

On first blush, here's what I can gather:

1. The surge is perfectly cyclical, which means it's not any sort of intermittent or transient fault.

2. The excessive slop in the slack side of the belt is synchronized to the rotation of the SC. This allows us to eliminate stiction of other accessories on the belt. The cycle starts when the marker on the SC pulley is at approximately the 7 o'clock position, and completes in 1 full rotation.

3. Factoring in item 2, would lead me to believe that there is some sort cyclical variance in the parasitic drag imparted onto the system by the SC.


Jeez, I need to wake up more to speculate any further...