When the TR1 turns the motor left or right it creates interference. Hummingbird call center won't put me thru to a real tec to answer my questions. Maybe someone here knows. It's has to do with the NMEA between the two. If I pull the com cable off the 899 the interference goes away. Both units are hooked up to a separate power source, yet the ground from the tr1 and the ground from the com are hooked together. Could this be the source of the interference? Running out of patience with the Hum help desk!