Hi Rick, thanks for the heads up,you were right about the bolt being too long, I just switched mine out with a shorter one and the plate is nice and tight now but it still pops!
Here's the problem! I took a look at the pulley attached to the back end of the Y axis motor and low and behold there's a small crack running vertically up the teeth. Good thing I have a few extra pulleys. Seems like and easy fix now!