I have the PT-100. If you use the USB from the PT-100 connected to the USB port of your computer you may experience a humming/buzzing sound coming through your speakers. This is to do with the USB port on the computer, I believe, causing a ground loop issue. I had this problem when listening to music and found it quite irritating. To resolve this issue I went online, did some research and bought a USB isolator. You connect this isolator to the USB port on your computer and plug the USB from the PT-100 into the isolator. This will completely remove the buzzing/humming from your speakers. I put my ear right up against the speaker and it is now dead quite. I bought the hifiymediy.com isolater. It costs $29.99 USD. and it is well worth it. Just wanted to share this info. with others who may have had or will have the same issue.