Answer:
If both transducers are of the same frequency this will occur. The only thing I can suggest is to try and run a transducer off the bow mount trolling motor. This distance will often reduce the interference. You could go to a 50khz and a 200khz transducer. Then the units will run with out any interference. The problem with the 50 khz transducer is the signal length which is very long and your target separation will be reduced. The 50khz transducer is designed for very deep water (normally saltwater applications).