I used a laptop to test my setup and it worked perfect with no interferance at all, Then i plugged it into a serial cable wich is connected to the onboard diagnostic port on the car, and i started to get interferance. I also then attached a power inverter to a wall charger for the laptop and that produced even more interferance. THe more calbes i connect the more interferance i get. I also hear the processor sound through the speakers.

What can i do?