I have 2 x Orion TR smart 12/12-18 isolated chargers fed from a start battery which is connected to the boat motor/alternator (see lousy picture attached). 
One charger feeds the house batteries and the second feeds the electric troll motor battery pack. House system works fine. Electric troll motor battery pack is 4 x LiPo 120AH in parallel feeding a 12v to 36v transformer and onto the 36v trolling motor. My problem is I am getting interference on my depth sounder which is powered by the house batteries when my electric trolling motor is running. I have tracked the source of the interference and it is coming from the output cables on the electric troll motor charger. Ie if I disconnect the +ve and -ve cables on the Orion for charging the electric troll motor batteries at the output side the interference stops. Note if I only disconnect either the +ve or -ve the interference continues. This seems to indicate the interference is being passed back through the charger, to the starter battery and onto the house batteries which I did not think was possible given it is galvanically isolated? The electric troll motor pulls high currents (up to 120A at 12v) so I thought it might be inducing a voltage in the output cables however I ran a new cable well away from the others and no change. Anyone got any thoughts? Is the electric motor causing a messy signal and I should try a ferrite core? I have the jumper in for the remote switch so using the engine detect function - not sure if this is relevant. Thanks in advance for any advice.
