Does this sound like a ground loop issue to you?

[Sigma]

Please read this post in full before responding. Sorry if it's a bit "TL/DR".

I built a new Ivy Bridge-based computer. I hooked up my mixer to the line in input of the on-board sound card, but when monitoring the input I could hear unwanted noise when my speakers were cranked up high (with no music playing). It manifested itself as a ticking noise and on top of that is like a high pitched frequency that fluctuates in pitch.

I assumed that the on-board sound was just crap, so I bought an internal PCIe sound card. When monitoring the line in input, the same thing occurred - weird unwanted noises. I returned that card and bought a different one, just in case - same problem.

Now, the weird thing is, that if I connect just a cable to the line in input - with nothing actually connected to it - the PC detects that something is plugged into the socket and I can monitor the line in input. This time, no weird noises are heard, but as soon as I plug the other end of the cable into my mixer - even with the mixer powered off - the weird noises return.

I am now using an external sound card for everything (a Native Instruments Audio 6) and the unwanted sounds are gone.

So, does this sound like a grounding issue of some kind? If so, why does it not happen with the external sound card? Does using an external sound card somehow "fix" the grounding issue? Even though the problem has been effectively solved by switching to an external sound card, I would still like to know what was causing this.

Thanks!

[ezelkow1]

Sounds like it if an external card fixed it. The external is going to have all of its components isolated from whatever is causing the noise either inside your case or coming from your mixer since its only connected over usb and transmitting data which wouldnt get affected by the noise. I remember having some similar situation during a live broadcast where we had to use an external card instead of the internal as a quick fix for a ground loop

As far as fixing it :shrug:

First try plugging your mixer or whatever else you are attaching to the line in to the same power strip/supply/etc as the computer itself, sometimes it works if all the components then have a common ground through the same power strip. Alternatively if you are already doing that, switch it and hook your mixer/speakers up to another circuit if possible, since the computer could be leaking noise back out on to the ground.

[Sigma]

Thanks man, but unfortunately that isn't an option. All my gear is set up in a spare room and there's just one wall socket. It's all hooked up to a Belkin multi-plug adapter/surge protector.