One of the units developed a clicking sound when it oscillated. I took it back and exchanged it for another one. After a few minutes it developed the same clicking problem. I took it back and decided to give it one last try. Unfortunately, that unit developed the same problem after only a few minutes of use. I took it back, got my money back and went to Sears who also sells the Bionaire products. They were out of the AP1500-U PERMAtec Ionizing Air Cleaner so I purchased the BAP2000-U PERMANENT FILTER AIR CLEANER W-GALILEO which wa... read full review »