First question, are you hooked to trolling batterie if not check routing of power wire and make sure it is as far away from motor power as possible. Then check the metal screw together connector from adapter cable to trolling motor cable. Make sure it is good and tight. Have seen that a few times where it was a little loose and caused interference. Last pull top cover on motor and check fuse to make sure it's not blown. You can lower motor to where prop can turn without hitting anything. Turn it on low for a few seconds as you play with different things to see if it goes away.
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Charlie Weaver USN/ENC 1965-1979