Noisy Quiet One Water Pump

hi-
i have a quiet one 1200 water pump that i use in-tank to drive an internal canister filter (fwiffo designed: http://www.aquariacentral.com/forums/showthread.php?171231-DIY-Internal-Canister-Filter!!!)

but now the pump sounds like a rock tumbler. the impeller sounds like there's sand or grit or gravel in there. i washed out the impeller well and cleaned the impeller. yet, the pump still sounds like there's something hitting the impeller. so i am looking for any way to remedy this problem. thanks in advance!

hi- thanks for the replies. ive been very busy with work so i couldnt get bakc sooner. the shaft is metal, attached to the pump housing. the impeller spins on the metal shaft freely through magnetism when the pump is plugged in. the pump starts quiet after i wash it out, but then it becomes noisy and sound slike a rock tumbler. so im not sure. i washe dout the impeller insides where the metal shaft goes and washed out the well of the impeller in the pump housing. still nothing. the air purges after roughly 30 seconds. so i dunno. im dissappointed though. darn thing is compelling me to get a better pump, an eheim, but i dont want to spend 100 plus dollars on a stupid water pump, ya know?! good grief!

hey- wow i became so busy i nearly forgot about the thread. i wasnt sure what the issue was, so i ordered a new pump and impeller from drfosters. i tried taking the pump apart, but the shaft was attached to the filter body. but it looked ok. i think sand was in the impeller housing itself. but thanks anyways for all the tips and help!!! you guys are great on this site!