Most folks say to use 800khz in the shallow water but I get trolling motor noise on the screen in 800 but not 455. I run a tiller boat so unit and motor are at back of boat, motor is a minn kota vantage 24v with batterys up front and wireing ran on oppisite side as HDS8 and SS box. 12v is supplied by the cranking battery which is at the back of the boat. Any suggestions or thoughts, thanks.