Sorry.

I've never heard a pump make a noise like that. It does sound like something is striking something else.

How does the sound change when you turn the pump off? Can you localize it better then?

Regarding fouled impellers, my experience has been that, if I couldn't reach through the port behind the basket, and drag the debris out with my fingers, that the pump had to be disassembled to clean it.

Good luck!