I have the same problem, but I don't think the collar is loose and causing the clunk. GC provided rubber O-Rings to prevent this from happening. I had to force the collars onto my MS struts because they were so tight.
It seems like (in my case at least) that the spring is just bouncing around when it loses contact with the perch and then re-seats, and of course you've got steel hitting aluminum... which causes an awful sound. Luc St. Pierre seems to have solved this problem using Nylatron shims on his perches to give it more cushioning. He told me that if there's enough interest in these, SRD could machine some and sell them.
Would anyone be interested? You can read the write-up here:
http://www.mx3gsr.freeservers.com/gc.htm
I'd like these to be made, so please post if you want some.
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