I did a water change about two months ago. With the water change I clean up the filter cartridges. After the cleanup, I refilled the filter and turned it back on. Then I heard sort of a "clinging" noise, as if you put a small piece of rock in a plastic container. I changed the impeller and it still does the same noise.
As you mentioned, I did 1 and 2. #3 I don't quite understand.
Thanks for the welcome, I have been to this site many times and finaly registered. I quite enjoy it. Happy Holidays.