Look in the nav manual and find the location of the GPS sensor / antenna .. it could be located near one of your windows and if it's trying to get a reading through the glass -- you are right the tint is probably the problem. Also doesn't the Honda GPS rely on a compass as well? I believe so because the nav system will still function without a GPS signal as it knows the relative speed and heading of your car (as long as the starting point is known) .. perhaps the metallic tint is messing with the internal compass somehow. Just some thoughts .. --Brian