There have been some threads around the web about issues with the receivers in the Xi series GTN GPS/NAV/COM units.   It has been traced to the squelch settings. Garmin just released updated software for the units (20.42) that increases the range that the Carrier Squelch can be adjusted to. A couple of guys over on BT, who are professionals in radios have tested things and come up with some recommended settings. If you do not have 20.42, you can still help your receive performance