My unit seemed to make a loud humming whenever it was used on Speed 2 or 3. I also replaced the carbon filter because the light was on and I cannot get it to reset. Since the item is under warranty I contacted customer service and was graciously helped over the phone within 1 day of emailing Pure Enrichment! Looking forward to my replacement and then will update my review as I was pretty happy with it (sans the two minor inconveniences).