Is the computer inside the house the same exact setup as the one in the car? Are you using USB audio in the car?
To say it doesn't do it on the home PC, but does in the car PC isn't a fair comparison. There are a lot of different variables (as I'm sure you're well aware) so it's not usually a straight apple to apple comparison.
I recall some issues with USB Audio - in my previous setup I used the USB Hub to do audio, and it would randomly mute the speakers upon resume/cold boot.