The old belt I took off it was bouncing It was stretched about quarter of an inch so I figured putting on the new belt it would stop that bouncingThe belt is too short or you are routed wrong making the same effect. The tensioner is bouncing. I had the same effect trying one of Gates RPM belts. I added larger steel idler pulleys that took up some legnth but when I tried an RPM belt (no stretch at all) I got the same thing I see in the video, swapped the belt and its gone.
Do you have a previous belt. If you made a change reverse it.
People assume that everyone knows all the abbreviations. Here you goSorry what Tensioner is that ars ?