scrolling horizontal lines on screen....interference?  

Need a bit of input on this one. I have a Benq projector being fed by both an htpc and a stand alone DVD player. Both are running through a vga switch and vga amplifier, the dvd player is connected via a component to VGA cable while the htpc is strictly VGA. With the standalone DVD player I am getting barely visible horizontal lines that move slowly up the screen every few seconds. With the PC I am getting the same thing only it is refresh rate dependant. At 60hz it's very visible, at 100hz it's barely visible but still there. Either way the lines from the htpc scroll alot faster than with the DVD player. Is this some sort of electrical interference problem? Any help is appreciated.

Well, I found the source of the problem (sort of). I have a PVR-150 card in the computer and I found as soon as I disconnected the coax, the lines went away. I'll have to see if I can localize it any further but at least I can watch movies without being distracted now. :) Thanks for the assistance!