My Penguin does the exact same thing. Thing is, I've had it about 2 months or so, and it only just started making the noise a week ago. I've cleaned it, taken it apart, and tried everything you guys have suggested (in this thread) and nothing is working. It's bugging the (insert expletive here) out of me!! It'll do it off and on for about an hour, maybe more, then be silent for an entire day. Or it'll just be off and on all day. I've taken to unplugging it at night because I can't sleep with the noise. I know I shouldn't unplug the filter, but it's driving me absolutely crazy... I had no problems whatsoever with it for almost 2 months, now this... I'm completely lost on what to do. Maybe get a new filter?
