i have all aquaclears (i have a 200 i believe on my 20), very quiet. all i hear is a soft trickling water sound, and thats if i'm really listening for it. i had box filters with air pumps before, drove me batty. i now have aquaclears on four tanks. you just have to be careful not to run it while its dry (will burn out the motor), and they don't have a switch so you can only turn them off by unplugging them (pain when the power goes out, lost one filter motor that way......................). fosters and smith usually has them on sale, and even with shipping, they've been cheaper than in any store around here.