Why does the fan get louder after only 1 week of use?
I purchased 4 of these BAP600 units from Best Buy just over a week ago. When first installed, the fan on each was quiet, especially on setting 1. Now, just a week later, all of them are much louder and the fan sounds much faster on level 1. They are all different sounding. One of them is so loud, that there is barely a difference in fan speed 1 and 2! For fun, I removed the filter and ran each on level 1, and the fan returned to the original quietness, until I put the filter back in. Cleaning the filter as per instructions has not resolved the issue.
Any ideas? There are no obstructions in the intake or outlet for air.