AAAHHH! The AquaClear hum and rattle, I have only used AC's Since the 90's. What you're hearing is most likely the lid, the motor does cause some vibrations, and the lids (being plastic) do not always sit perfectly flat and flush. Thereby causing the lids to rattle and/or hum. Simple fix; put a rock on the lid. Or do what I've always done and just leave the lids off!!! Problem solved (for me anyway). Hope this helps.....