It would be best if you could figure out where the signal is being picked up--the wire from sound card to amplifier, wire from amilifier to speaker(s), power cord to speakers, the amplifier itself, sound card, etc.
To block RFI from wires, you use ferrite cores which you can get from electronic parts vendors (e.g. Radio Slack or on-line like AllElectronics).
To shield the sound card, take some heavy-duty AL (aluminum) foil or fine-mesh CU (copper) or AL screening and coat the side that will be toward the sound card (and wrap some around the edges of the foil or screen a little and protect any other surface that might come in contact with other boards or the mobo) with a double thickness of plastic wrap (original Saran Wrap is best) or heavy package tape. Make a little tab in the foil or screening of double or triple thikness to fasten to a nearby screw (like the one that holds the card in) for grounding. Use a washer under the screw head to avoid stress on the foil. Try it covering the back (wiring) side of the sound card first. If that doesn't help, try it on the component side of the board, still nothing, make one that wraps over (or around) all sides of the card.
To shield the amplifier (might have to open up a speaker to do this) make a cage from fine mesh CU or AL screening that will completely surround the amplifier components. All edges of the screening must be bonded together with solder and a wire soldered to the cage that will be attached to ground. Protect form shorting components as above. Alternatively, you could try wrapping as much as possible of the outside of the speaker that has the amp in it with heavy AL foil or screen as above which will work better if you can find a way to ground the foil. No warranties or guarantees expressed or implied with any of this <g> .
.bh.
Facebook
Twitter