Help with Garmin troubles.........

[Ice Cream Man]

Currently have Garmin GPS/Map 2006C & Garmin GPS/Map 198C......
Transducers are on opposite hulls - Cat boat.....
Picking up interferences & not getting a clear picture of the bottom.......
Makes finding bottom fish difficult........
Tried turning one off, tried setting to different frequencies - no improvement in imagine

Maybe using a better transducer?
Any suggestion on how to correct this problem.......Thanks...........ICM