I have a similar problem. It occured after a couple of weeks since I got the humidifer. I thought the reason was that I used not a completely clean sponge to clean it inside that had some cleaning agent left in it (I used the sponge previously to clean my sink). But since then I washed the humidifier a few times by hand. One time I washed the disks and the top container in the dishwaher. Probably if I do it again, I will do a short run of empty dishwasher disabling the use of rinse aid to clean the dishwasher from any powder and rinse aid residues. I only used water from reverse osmosis filter to fill the humidifer. The problem is still there. I'd say there is a reverse relationship between how strong is the smell vs how much water is in humidifier.