Head making sound as if a screw is rattling around when flushed

Oct 8, 2013
46
Hunter 356 Connecticut
Hi,
We have a Hunter356. Our head is fresh water, flush. When we flush, it sounds as if a screw is rattling around in system. Sort of like when you get a stone in your hubcap and it rattles..This just started this weekend. Any thoughts? Thank you in advance. We know nothing went down toilet.

Lauri/Norm