I would have thought the above bar would have cleaned up any EMI on the line apparently not but then you say your speakers also give a loud click pop click when you turn on you PC which leads to the conclusion your earthing is crap call an electrician to sort out your bad earth wiring
So I just tested the outlet with a little yellow outlet tester... the ground is fine, but the hot and neutral are reversed. So that's why I get an electrical shock if I touch the metal casing of a recessed lighting fixture when I'm changing a lightbulb with the switch turned on. Don't know if that has anything to do with my issue though.
I should probably mention the loud click pop click only happens when the speakers are actually plugged into the sound card.