VGA cords are very thin.. the shielding is.. so so. Almost anything will cause interferece. If you HAVE removed power from the RF unit; then the signal interference it causes SHOULD stop, but you might also want to try moving the antenna out of the car to make sure (large hunks of metal... but I dont see why THAT would effect it and not the car chassis)
Ariel loops, strange TV antennas have a way of creating strange ****ed up fields- but usually they need power. So I donno
Even if it doesn't stop the interfere, you should really hardwire it to your headunit man.