hello all, i'm new hear and to the fish stuff. i'm learning fast though. well i have a 90 gallon tank and a aquaclear 500. when its turned on anything higher than the lowest setting it make this clicking noise. like there is something stuck in it or sand. but theres not i cleaned the crap out of it and it still make the noise. today i somehow got it to stop but i unplug it because i had to plug my christmas tree in and when i pluged it back in it started clicking again. what gives? anybody else have this problem or have a clue on how to fix it?