How do I check that my motherboard is properly grounded? I am getting unwanted sounds in audio recorded via my USB audio interface, especially from sources connected to external devices with their own power cords (e.g. my bass amp), and I am trying to see whether some problem with grounding of the motherboard or other components is to blame. I have been trying to bridge various places on my case to ground with a voltmeter, but I can't find anywhere on the case that isn't painted, and in any case I'm not knowledgeable enough to know whether the case being grounded would automatically mean that the motherboard was grounded too. On the other hand I don't want to ignorantly poke my voltmeter in the wrong place and damage the computer. Can anyone tell me what I am supposed to do? Thanks in advance.