I dont have the setup in the car yet BUT I am picking up hiss especially when the computer is turned on.... The hiss is there running off the invertor and running off 240v mains.

There is less hiss when the computer is turned off.

My power cable to the amp is 1.5metres (unshielded).. could this be the problem? It will be shorter when it is installed.

The soundcard (SB pci128) is connected to a sheilded 3.5mm>rca connectors. This is connected directly to my amp (Caliber CA 80wx4channels).

HELP please.. :O)