When first starting the car on a cold morning, you get a radio interference & sat nav goes off when revved. It only happens when it is cold, so I'm guessing it's related to either something dragging power that helps start the car on cold mornings. Like the glow plugs, or the is a over drain on the battery that the alternate can't replace quick enough. But after about 2 minutes it seems that the power has Been replaced in the battery. Or the plugs or something is no longer required so does not interfere any more. I tend to leave car ticking over and do not over rev for the first 2 minutes & then it is OK. Does not happen in warm weather. Might try a new battery if it persists. [/b]