xyz daVinci Pro - Y Motor Belt Tensioner - Bruce Walker

Yesterday while investigating a sound in my daVinci Pro I found one of the tensioner pulleys in my printer dancing more than I thought it should. Today I took the machine apart to investigate. I did not see any sign of damage/wear, and the belt did not appear noticeably loose. Examining how the pulley carriage engaged and moved in its mount I cannot honestly figure our how the pulley ever didn't move around as much as it was moving around.

Since I do not want the pulley to move around so muc