Yep, it's a result of the left ramp design. Because the flap sticks out past the entrance, shots that just barely hit either post will already have an upward trajectory and do that rejection thing, banging off the ramp cover. I took the cover off, but all that does is allow these post shots to carom off onto the plastics. Especially on the left... you'll think the shot is good but it'll clip the metal protector and bang around, except now the rattle goes up/down in addition to left/right.
There's another thing that might be happening.. a clean shot that hugs the wall on either side of the ramp will first hit the screw hole in the flap, and then catch the edge of the flap rivet. This could also lead to rattles into the cover. I mylared over the hole to help mitigate, and want to eventually grind a bit off the rivets so the ball can't hit them. Same with the screw in the tower ramp approach.