Just like a whale.
I am happy with this humidifier because it is very pretty & puts out a lot of moisture.  The reason it does not get five stars, is because it is too loud for me to leave on at night.  During the day however, I enjoy the soft gurgling sound.  Sometimes it makes a slightly louder buzzing sound until my husband comes to give it a gentle shake & then it's as good as new.
Rating: 4 stars