@tconcepcion,

The HS220 is listed as being compatible with the following dimming types:

Dimming Type: Leading Edge Dimming / TRIAC Phase Cut

Also ensure that you have completed the dimming calibration in the Kasa App, as this will narrow the power at which the light functions. Without bulbs it would be impossible for the device to know if its sending too much or too little power. It may be that these lower buzzing noises are too low to support the fixtures. Please check both the fixtures and the bulbs for compatability