Gremlins

At a compete loss here on an odd electrical problem that I was going to pose to the TW community for any leads on a solution.

COMPONENTS AT PLAY:
- Hella Supertone horn wired directly to battery with fuse block and relay. Relay is attached to the OEM horn wire
- Hella Sharptone horn wired using OEM wiring

- JVC headunit
- Kicker Hideaway powered sub

ISSUE:
- When the Supertone horn is blown for more than just a "tap" then the JVC headunit will instantly increase to MAX volume with heavy, low frequency disturbances
**Does NOT happen if the Kicker powered sub is not powered on/disconnected
**Does NOT happen if the Sharptone horn is the only horn in use

Issue appears to be interplay between the Supertone horn and the subwoofer.

I have checked all grounds and took the steps to ground all components directly to the battery and each ground combination I attempt returns the exact same results.

QUESTION:
Does this still sound like a bad ground issue or a bad Hella horn? (ordered a new Hella horn already to test but not there yet)