Humming noise

If this is like my unit it is a high pitched squeal. I received my unit as a gift for Christmas 2007 and I thought it was defective. I contacted Homedics and they sent me a replacement but the problem persisted. As licensed amateur radio operator I am versed in electronics so I decided to track down the source of the noise. It turns out that the 16VDC power adapter is the source of the noise. It is what is called a "switching power supply" and is unfortunately not well filtered causing the high pitched squeal. I was able to get rid of the noise by modifying the power adapter and adding a 2200 microfarad capacitor in parallel with the output. This filters out the high frequency ripple and gets rid of the squeal. An alternative solution would be to search the Internet for a better 16VDC power adapter. It must supply 2 amps of power and have a 5.5mm OD/2.1mm ID center positive power connector.