You've probably resolved this already. I had the same issue. I tried securing a rubber bicycle tube with mini screws but no success. I then used a piece of sound deadening rubber that I bend and adhere at the same time. This was key as I installed, removed, installed and repeat again that assembly
It seems to be working okay as for any rattle. Please let me know your solution as I am still struggling with the correct adjustment for the window and it maybe that guide assembly.