If it is I have never heard a difference. Maybe with a meter of some sort you could differentiate the sound difference. The biggest difference is using soft tubing on your return pump to limit sound caused by vibration. I have a room full of tanks and its loud mostly from the overhead sumps and air pumps running. If I shut off everything but my reef tank its pretty quiet. I get a trickling water sound in the pipes its very little though. A little sound from the overflow which I could lessen if I brought the water level in the overflow up some more. A slight burble from the drain pipe into the sump and a slight hiss from my skimmer pulling air. 5' away and almost nothing. Mine is all hard plumbed.Thanks. I read somewhere that the flex is quieter than hard pipe but I guess it depends on how many and what type of bends you're doing (90's, 45's, etc).