I had an ip3500 and often when I jostled it even slightly, even just barely touching the top, it would start to make noises as if it were self-cleaning. Presumably for some other reason it broke and I had to replace it with a "new old stock" unit of the same type. It was nice to have some degree of quiet for a few weeks, but now it's started up again! Any ideas what is causing this odd annoying behavior and how to stop it?
