Recording noise with microphone unplugged

[xix]

Hi,
I use an LD systems USB microphone, and while recording, it has a slight noise. I noticed that it is present even when I unplug the microphone. I use Audacity, and tried all input sources (Realtek High Definiton Audio, Microsoft Sound Mapper), and it's the same on each of them.
Spectrum analyzation shows that it is close to a white noise, so it's not a grounding problem. My best guess is that the default (analog) microphone port is always enabled and acts as a radio antenna, collecting electromagnetic pollution.
[video="https/www.youtube.com/watch?v=XLoOEKQPKSw"][/video]
Can anybody have a guess?

 

[jensrobot]

What kinda soundcard do you have? if its onboard it's pretty common. Also, if you use front headphone jack on your cabinet, chances for noise is higher.
I don't think your mic is in listen mode, you can check that in audio settings. I'm not sure about this, but if memory serves me well, the AC97 standard has your audio outputs activated all the time. Dunno how this affects the mic input, but maybe its smart enough to not use it when nothing is plugged in... still if listen mode is not activated it should not matter.

Is the sound like this even on longer use? - is it pure white noise all the time? if it changes while you do other pc tasks is a interference signal somewhere from your pc. If its a slot soundcard, you could try another slot.

Just brainstorming here, apologies if some of this is trivial or if i'm off by miles