Have a look at the map disc and see if it has any surface blemishes too, this wont help, Also if you have a cd map try that, and see if the problem goes away.

__________________
Sept 03, M3, Silver Grey. Retro-fits: Modded Mk4 DVD Drive, OEM Bluetooth, VR Control, Rainbow Speaker Upgrade, Sony SOT Amp, HK Sub, CCFL, Intravee II, NightMode.