The problem was there before I got the monitors, it was only less obvious. The soundcard is the wamirack 192l which has the same converters as the 192m. I run the card to a mixer in a balanced configuration and then to the monitors. The noise is there when I monitor with headphones on the mixer. I guess my card has a problem, there's 2 week left on the warranty, I better hurry...

This sounds like a wiring issue to me. What are you using for an amplifier? Does it have unbalanced inputs? I am suspecting that your sound card is balanced outputs being connected to unbalanced inputs of your amplifier. Here's a quick way you might be able to elliminate the problem. If your amp power chord has the 3rd pin attached, then get a ground lifter adapter and then plug it into the outlet and see if your noise disappears. If the amp doesn't have a 3 pin power chord, then check your PC, that should. Again, get the ground lift adapter and plug that into your PC's power chord. One of those MIGHT fix your problem. The proper way to do this is through the actual wiring from the sound card to the amp.

Something is going wrong with the common mode rejection that happens in balanced outputs, to reduce noise. Another problem might be that the sampling frequency signal might be coupling in on the DAC outputs of the sound card. Not much you can do about that one, moving the card to a different slot might help, if it's a PCI based card.

Thanks. The cards goes in my mixer through a balanced configuration and then to my monitors unbalanced. The noise is present when I monitor int he mixer using my headphones so I don't think the problem is with the monitors...

Where's the amplifier? Iin the mixer or are they self powered monitors? Have you tried unplugging the monitors and then listen through the headphones. Just because you currently hear it through the headphones doesn't elliminate everything beyond the mixer. It only takes 1 device unproperly ungrounded within an entire studio setup to make the entire studio buzz.

Is your mixer and PC plugged into the same outlet? Do they both have 3 prong power cords?

They are self powered monitors (behringer truths). I monitored using the mixer and headphones with the same results, with the monitors unplugged... All my signal chain is balanced. All the stuff is connected to a surgemaster all with 3 prong cables, the main outlet is grounded also...

I would disconnect everything from the sound card, then plug in a set of headphones directly into the sound card outputs to see if you can still hear the same noise in the headphones. You will only hear one ear of the headphones, but that will be enough. If you hear it there, then I would move the card to a different slot on your motherboard and do the same. If you still hear the noise, I would expect there is something wrong with your sound card. In audio hardware there are many capacitors and inductors put in place to elliminate noises being generated by the digital circuits and preventing them from being coupled into the audio signal. I would expect there is either a bad capacitor or a solder bridge allowing the sampling rate word clock to couple into the audio signal chain. You can see this same type of thing sometimes in Laptops with onboard sound cards, where when you move your mouse you can hear noise through your speakers. That's because the sound card A/D and D/A converters are very close to the digital circuits and the mouse is generating digital signals within the hearing spectrum, and these signals get coupled into the audio circuits. Without actually have heard the sound you're experiencing, from your description this would be my best diagnosis.