I would wire as Rickie directed.
Not sure that this will cure what you are seeing but it is the first step to take in a (possible) multi-step process.

If that does not clear it all up than you could try turning up the Noise Filter in your 596c DI unit.

If that does no provide enough help than try getting out on the lake a drift so that you can rev the motor while it is out of gear to see if that makes the interference show up or not. if it does than make sure you are running a resistor type spark plugs in your 25hp motor. You may end up needing a separate battery to power your 596c DI unit from.