Hello David,
perhaps the fix parts of the perspex screens shakes or rattles a bit in their guardrail?
I had this problem on one of my sidescreens.
The minimal gap between the perspex and the guardrail was almost unvisible but when I held the whole sidescreen with one hand in the air and beated on it with the other hand I could hear the rattle sound.
It took some transparent silicon gel to be shot in the gap, some time to let it dry and the rattle was eliminated.
Perhaps this could the same source of rattle and it may also help on your screens.
Kind regards,
George
