I have noticed on some of my tripod mounted images with 5D a strange noise pattern, which with help of some of you was identified as RF noise. here is the link to that thread http://photography-on-the.net/forum/showthread.php?t=508539
This happens if you are standing very close to your camera. I figured out how to avoid this which may be obvious to some of you. If you enable mirror lock up, and put the camera shutter on remote/timer. now when you press the remote button, the mirror moves, but exposure does not start for another 2 seconds. I have been able to avoid the RF noise doing this.