Trolling motor interference

I have a Humminbird 998C with the Hi Def SI transducer. It has been on there for a couple of years. Just the last two or three trips my depth with almost double the actual depth when the trolling motor is running. Example: if actual depth is 25', it will show 25' until the motor is used and then it jumps to 50'.

I have played with the sensitivey and other settings. Any suggestions?

Thanks

If you haven't moved any wires or done nothing with the fish finders I would then focus on the trolling motor. Something could be bent, string around prop or worn brushes.

Add damaged transducer cable to the list.