It could be the Nav hard drive.
Is the car stopped or moving when you hear the sound?
Is your Nav zoomed all the way in for the map? This causes the drive to work harder as it tries to keep the vehicle position accurate on the map. Zooming out result in less constant adjusting. So maybe just a little noisey hard drive.
2013 VW Golf TDI
Last edited by chuck92116; 02-23-2013 at 12:29 PM.