Yes, analog traces can cause this problem. If you can attached the schematic and layout here I'll take a look at them. Let me know if you want to take this off line to be more confidential.
A lot depends where the 75 Ohm resistors are placed and if you keep the analog traces as 75 Ohm impedances.
The analog video is from a 75 Ohm source and 75 Ohm impedances must be maintained right up to the 7604, through the cable, connector and traces.
