I just installed the Xi5 and the GPS signal is interfering with my humminbird 1198 and 788.
The units are clear when the motor is off or running at high speed. Interference comes when I hit spot lock, so I'm thinking it's the GPS but it may be the motor itself. Here's what I tried:

Shut off one unit.
Run the units on separate batteries.
Adjust the noise filters and sensitivity.
The wires for the units are on the opposite side of the motor.
Made sure the motor is not vibrating.

is the humminbird unit wired direct to the cranking battery?

Yes, both units are. That might be the issue?

I just wired the units directly to my batteries. It got worse
I'm open to any suggestions, thank you.

What does that mean "directly to my batteries"

I ran a separate line from the battery to the units, there were wired into the console.

Watch this video where he talks about tuning the noise filter on the unit.

RFI is random in occurrence no matter what sonar/GPS brand/model or motor brand/model and which frequency is affected.

You have two motors that can be the source, the trolling motor itself and the steering motor.

Call Humminbird Customer Service for assistance with dealing with your RFI issue and describe your installation.

If you ran the transducer cable through the coiled power cable, that is a good place to eliminate also.

My Onix is doing the same thing with Xi5. I haven't attempted to track down the problem yet. I plan on trying a noise filter.

Try installing some ferrite beads on the power leads and sonar cables going to your Humminbird. You open the ferrite bead and make one wrap then close it over the wires. I have used this successfully on lots of Ham Radio and other electronics to take induced noise out. They are cheap and you should be able to find that at Radio Shack, Frys or any electronics stores. I would install one on each end of both cables.