my mom's 400 does this alot, and what i usually do is just kinda halfway unplug it to make the motor stop then start again then it's usually fine. OR what could be wrong is that the impeller has something in it and needs to be cleaned. other than that, her 400 is always peaceful.
Thank you. I tried that little trick where you play with the plug and it finally got my e400's to STFU.
My filters are usually noisy for a while after I take them apart for a cleaning. Then a after a little sludge build up they're really quiet. Now that I know that trick, they'll be quiet all the time. Thanks again.