Garmin Nuvi 660 GPS Receiver "car audio hear callers" Questions

audio output to my car speakers via the 660's FM transmitter. The echo stays with the caller even if I turn the car radio off (i.e. the echo is not caused by mic-loudspeaker feedback) The echo is less

...audio either through the phone or the car speaker. I cannot hear the caller or vice verse. This is the case with either calls I initiate or received calls. I need to move 50 feet outside the vehicle ...