Try removing the TM batteries from the 3 bank charger...

If the interference goes away...the RF is being generated somewhere around the charger area...and bleeding into a nearby sonar power cable or xducer cable...

If this is determined to be the area of RF generation...the easy fix would be to have the TM battery charger also up front with the TM batteries...

And then have a separate 1 bank charger in the rear for the unit battery...

Rickie