USB Connection to Multi-media Projector

When I use the USB connection on my Inspiron B-130 laptop to an Epson EX70 Projector the sound on the DVD slide show breaks up. If I connect with the video cable the sound is OK. Does anyone know what is causing this? I have tried different USB cables, tested all of the USB ports and Epson replaced the projector in case it's USB port was bad.  MMD