Just recently built a new PC. Don't have an external DAC or a soundcard currently, so Im just using the onboard 3.5mm output to RCA to drive my active monitors. When the speakers aren't plugged into the computer there is a very faint hum, but when I plug them into my computer the hum and crackling gets very loud and listening to audio from the computer is almost unusable. When I plug my monitors into an iPad or MP3 player I do not get any hum or interference what so ever. Unplugging my monitor via HDMI decreases the noise coming from the computer but does not rid it completely. I think since there is no hum or ground loop when plugged into a source that is not my computer, the interference must be coming from my rig. What can I do to combat this? I was planning on getting a USB DAC, but if that isn't necessary I would rather save the money. Any help is appreciated. Thanks in advance.
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Severe Humming/Interference only through Onboard Audio
- Thread starter simon741
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Integrated components are prone to interference due to lack of shielding. Get an external sound card.
Try a different powerstrip, if you use one. try different outlet (bad ground at outlet) unplug any phone chargers and small ac/dc transformers. Did you skip any motherboard standoffs when you built your pc? old house with ungrounded outlets? try unplugging every thing on the pc's breaker circuit except pc and speakers. are you using a 3.5mm to RCA Y adapter? touch the RCA side when it's plugged in, hum stop?
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Many power supplies leak 120 volts potential to the chassis. This can cause nasty audio problems when your computer gets grounded through the audio shielding 
There's an easy way to find out if this is the case. Just keep your finger tip between your audio jack and computer while touching your computer. If you get zapped with electricity, you have a grounding problem. Since this zap makes current pass mainly through your finger tip you shouldn't die (I didn't) but I would probably pass on this test if I had a heart problem or a pacemaker
Make sure both your computer and hifi system are using grounded sockets and preferably are connected to the same wall socket.
There's an easy way to find out if this is the case. Just keep your finger tip between your audio jack and computer while touching your computer. If you get zapped with electricity, you have a grounding problem. Since this zap makes current pass mainly through your finger tip you shouldn't die (I didn't) but I would probably pass on this test if I had a heart problem or a pacemaker
Make sure both your computer and hifi system are using grounded sockets and preferably are connected to the same wall socket.