Does the noise continue when you use the mic with anything else that has recording/mic capabilities?
If it does, then there something wrong with the microphone. If it doesn't the it is probably with the game.
Well, the problem could be that upon launching "CSGO" your mic is automatically adjusted to be the at its highest sensitivity.
To fix this, please do the following.
1. Load "Steam", then go into "SteamApps".
2. Next click "Common", then select "CounterStrike:GO"
3. Click on "CSGO", then "CFG" and finally "config".
4. Open the "config" with Notepad or Notepad++
5. Now, in Notepad, click on "Edit" and then "Find Next".
6. Type the following in the "Find Next" window... voice_mixer_volume "1.0"
7. Change it to the ammount you...