Okay, this is my 3rd + problem in as many days... I just bought a used 20g setup and it came with a Marineland Penguin 300. I didn't test run it before I set the tank up, so I don't know if it had always made this noise or not. In the process of bleaching the heck out of it, my daughter stepped on the impeller. I doesn't look broken or bent or marked in any way, but the filter sounds like my dishwasher grinding food chunks! It is driving me nuts! Anyone know how to remedy this? The filter is completely clean, so I know it isn't a chunk of something in there.