I had a tech come out on Monday to check my airhandler because i was hearing it humming noise even when the unit is off. He told me it was the transformer that is making the noise, and that was normal. My unit is a Trane XL14i with variable speed. The technician adjusted the speed in the airhandler and now my airhandler is running with high speed and noisy. Before this technician adjusted the speed my unit ran at vaiable speed starting out with very low speed to meduim speed and low speed. Now i can hear my air hanlder all the time running. In the past the operation was very quite most of the time. I think i will call the company to restore the airhandler to the dafault setting when the equipment was installed. This unit was installed in March 2006.