I purchased two of these small space air purifiers after researching and looking at reviews online. They were far less expensive than others with lower reviews; however, I guess you get what you pay for. After about a month one of the units began to rattle when on. My husband said it sounded like the ball bearings in the fan that circulates the air. There is no way to get to the mechanisms to try to find out more. I had to discard the unit after a very short use period. The second unit seems to be working fine after several months use. I guess it is just the "luck of the draw" with these units, but a 50/50 chance of working is not really what I look for in a product. I will not purchase again, nor recommend air purifies from this company to anyone else.