Need Help With trolling Motor Interference !!

Last summer I bought a new 70# Powerdrive v2 with US2 and a Humminbird 535.I had the marine shop where I bought the boat install and wire the fish finder and trolling motor.I only had a chance to get the boat out 3 or 4 times before I put it away.Now each of those times I would get very high and erratic depth readings on the finder when I used the 24 volt trolling motor and it seems to get worse the more power I would give it.The screen would also get cluttered up from interference and depth reading would blink and reading would freeze up.Fish finder would work fine if I didn’t use the troller,(ALOT OF GOOD THAT DOES ME).The finder is wired to the cranking battery and the trolling motor is wired to 2 – 12 volt batteries in a series.There is an adapter cable that goes from the fish finder to the trolling motor for the transducer on the universal sonar.Does ayone else have the same problem or any ideas on what I might try to fix the problem? I can take my 383c off the power bracket and plug it in to the power bracket of the 535 and run high power on the troller and it works fine.If I put the 535 on the console power bracket it makes a clicking noise and background lighting fades in and out .Any and all opinions are welcome.My warranty on the fish finder runs out 4-14-08.I’ve ran out of options to try.
Thanks, Rick