|If this only happens when you touch the case I would suspect an incorrect grounding of the motherboard. Did you verify that motherboard standoffs are correctly positioned beneath only the required mounting holes of the board? If the case came with extra standoffs and you left them in place they could be contacting the motherboard in an inappropriate place.|
For future reference, when posting a question please include a detailed description of the system specifications including make/model numbers of the major components. ie, Motherboard, CPU, Power-supply, Graphics card.
In your situation, with a self-build, info on the brand.model of case might also be helpful. If you have used a cheap-build case it might be it has pressed raised screwmounts for the motherboard rather than proper standoffs. Those things occasionally need to be insulated when assembling the system to prevent unwanted grounding.
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