Check that fuse yourself and verify that it is OK and its connection is OK. Any further remedy attempts are more radical.
The interference is RF (radio frequency) and is caused by the motor variable speed electronics ( most of the time) there are no absolutes with that issue.
Your unit should already have the PC 11 power cord with the built-in choke. That choke is about 3/4" thick and 1 1/4" round, located 4" from the unit plug.
If you have Interlink, disconnect it for a while. That is just an antenna for the RF until you get it figured out.
There are a few "grounding" methods that may work sometimes when the previously mentioned motor internal ground wire doesn't.
Try putting a jumper wire (any size) between the negative of the battery you are using for unit power (starting battery ?) and the battery negative that your trolling motor negative wire (black) is hooked to. Don't connect it anywhere other than those two places. No NOT hook it to any of the other trolling motor batteries anywhere !!!!!! That is called a ground loop.
Report the results--there are a few more remedies available that may or may not work.
Let me know via e-mail so the suggestion turn around time will be less (well maybe not tomorrow, I'll be on the water with my 1198 trying to find some fish, LOL)
purdum43@aol.comAlso post a picture of the TM choke installation.
I spent 6 months dealing with that same issue with a Motor Guide.