Easy solution would be if you are running via head unit to just turn the volume down before you exit the vehicle.
Hi I'm using an external soundblaster for input into my amp
I have a carnetix P1900 powering a macmini and controlling the amp. The soundblaster is conected to the macmini directly with usb.
My problem is that when the mac mini is booting (if the car's been sitting for a long time or various reasons), the amp will turn on and I will get really horrible static until the mac finishes booting. When the mac does finally boot it is usually accompanied by a loud pop on the speakers when I assume the usb port is finally initiallized.
What can I do to stop this?
Nope, only the computer, no head unit.
Am I right in assuming this is because the soundblaster isnt grounded to the car chasis?
How do you have your Amp(s) powered? Is it via the ignition? If so, try moving setting it up so that the power is applied when your USB devices power up (or slightly after actually).
Alternatively, if you are connecting the SB directly to the Mac or to a non-powered hub, try getting a powered hub and run it off the P1900 directly so it is on when the car is on.
Also check the FAQs and threads in the Audio forums, i'm sure this has been talked to death over there as it isn't just a Mac only issue.