My TN SE didn't have a head unit. I've fitted one, using the factory speakers in the front, and some Kenwood 6" in the back. However, I have some MASSIVE interferance problems. Random thunks when electronics are switched in and out, rather heavy duty ignition interferance, and the same tone at random intervals with the engine off.

I'm thinking it could possibly be floating earths, but I'm not sure. Could anybody offer assistance?

Hey got ur pm - Erm what headunit is it?

Where did u ground it? Try running the ground directly the the chassis. are you using an external amp as well?

What have you wired up to it? Just speakers, power and ground?

Headunit's a Mitsubishi RX326A (The stock TP Elite headunit) but with no amplifier, just HU and speakers.

The earth is through the cabling, and the metal frame of the console.

well my first thought is the ground doesnt have the best path. Other than that the headunit might be cactus?

try relocating the ground