I purchased this humidifie a few hours ago. Followed the instructions to fill and use. Left it on while I went out for about 2 hours. Came home to a LOUD operating noise. Water still in the tank. This is not a normal operating noise and it wasn't present when I first turned on the maching. I'm about to return it to the Walmart I purchased it at, but thought I'd try this first. Very upset over this since it's a pain in the ass to have to return and deal with this. All I wanted was a humidifier that worked!!!!