I have several devices connected to a Matrix switcher. These include a DVD player and a desktop PC. The matrix switcher sends the signal over cat5 using Kramer transmitter and a PT120 receivers to the projector. The NEC projector produces a flicker on screen intermittently when changing from the dvd to the pc. The flickers only appear on screen the screen when the pc is selected. This leaves small black lines land and distorts part of the image. There are other devices connected to the matrix switcher and they do not display the flicker. Any ideas why this is happening?