Audio issues using HD as USB input

I am using the HD to input slides to the Webcaster X2 via VGA. The distance from the computer to the camera setup requires a long cable (24’). I have tried a longer usb with the HD near the computer and a longer VGA cable with the HD near the Webcaster. As soon as the VGA cable is connected I get a hum and a rapid high pitch beeping in the audio stream. USB audio is disabled and I have changed all input and output resolutions to match, which helped some, but the problem persists.