"Only worry is for the price I paid, I am worried of the possibility that the unit will make a noise I find hard to sleep with and requires a return. I sleep well with hiss or white noise. I don't sleep well with hum. I would expect at this price point, hum would not exist. Hum usually comes from the motor being mounted steel to hard plastic or wood. Steel to steel with sound isolating rubber gasket between usually eliminates hum as most hum is vibration related. Airflow noise through channels and fan blades is usually just white noise like a mountain stream over hundreds of stones makes. Got the unit. Has some hum, but okay with it. Nothing like an expensive Sears purifier I had 20 years ago."