clutch chatter?
Chatter and rattle are a larger concern with aftermarket clutchs because the "tuning "of the center springs is not generally very good( some have no springed stage at all).
It sounds like there may be a large chunk of something in one the friction pucks. It works fine and has been doing it for at least 20k miles so I don't worry about it. It sounds just like a dining room chair sliding on hard wood floor.



