Perfect for us
The constant &#34;whirr&#34; sound is definitely audible, but it is for the most part a relaxing sound and not bothersome.  It seems to do a good job knocking out catbox odors (I have it plugged in about 2 ft away).  Others complained about the lightbulb burning out very quickly, but I've had it plugged in for a month straight so far with no problems.
Rating: 5 stars