This question already has an answer here:
I have a brand new Blue Yeti USB microphone on a shock mount attached to a boom - no vibration noise possibilities in this setup. I have tested this in a dead silent enclosed room using a Macbook Pro with the fans on the lowest RPM (basically off). I have also tested using a desktop PC, and tested using a wall-powered USB hub. In all of these scenarios, there exists a subtle high-pitched hum that sounds very electronic and unlike ambient noise. What is causing it and how do I get rid of it? I've tried two different USB cords: one short and one long. Here is an unedited audio clip of the noise: https://dl.dropboxusercontent.com/u/7345145/noise.wav
The deep humming is probably my desktop computer fans - I'm referring to the higher pitched buzzing noise over it.
The gain is at the lowest setting on the microphone dials, and it is set to cardioid mode. The microphone level setting in Windows 7 is set to 22, though as I said I tried this on a Macbook Pro and heard the same electronic noise. I would really appreciate any advise with this, I'm at the point of pulling my hair out.
Edit: I ran a male to male 3.5mm headphone cord from the mic output to the line in on my Creative Titanium HD card input. At first test the results looked much better (and quieter) in the waveform, but after amplifying the levels to -0.1db for my voice, I could also hear the same electronic hum again. Here is an audio clip of the hum: https://dl.dropboxusercontent.com/u/7345145/noise_2.wav