I have taking all my grounds to the same point, I still have alternator whine. I have perfect audio with motor off. Start truck and whine starts. I can unhook the rca's at the amp and no noise. I know it is coming from the computer. I can even mute the computer and the whine stops. Everything is grounded to the same point. I use a usb sound device that is ran 8' away from computer. If I plug another source in I have no whine. Any ideas besides finding a 40 amp line filter. I can put a ground wire on the usb cabel end and get rid of 80% off the noise but not all. I tried ground the MB at several places no good. I ran a USB cabel over head no good. I unhooked the monitor no good.
Any ideas would help.