Whendriving, the navigation screen on my new 2007 S60 has horizontal interference lines. Looks like the interference you get when you run a vacuum or hairdryer on a home TV. Really annoying in evening hours and most noticeable in the blue and green areas of the LCD. When the car is off and you run the navigation in the key on position there is no interference. So it must be coming somewhere from the engine compartment. Anybody else have this problem.

 

This is just me but I would bring it into the dealership. Possibly a bad ground. But it sounds like its picking up RF (radio-frequency) interference or EM (electro-magnetic) interference from the alternator. It shouldn't be your job to troubleshoot/fix the problem. Make the service department take care of it.