Check the settings within windows and your audio drivers and you may find an option to allow a microphone "gain" or "Boost". Which will allow the microphone to listen more carefully w/o being set to max.
If you use Windows XP,
1. Click Start
2. Click Settings
3. Click Control Panel
4. Open "Sounds and Audio Devices"
5. Click the Advanced button in the Device Volume section.
6. Click options
7. Click Properties
8. Click the "Recording" radio button
9. Click "OK"
10. Click the advanced button under the microphone input volume.
11. Make sure there is a checkmark in the "Microphone Boost" box
If this setting is already set correctly. Then it could be a setting within the audio drivers software. If you are certain all settings are correct then you are likely getting "radio interference". It isn't always caused by radio signals but electronics can cause it too and almost any piece of hardware in/on the motherboard could be the cause.
You can either send the motherboard to ASUS for RMA.
Buy a sound card. (Sound cards tend to be less susceptable to this type of issue.)
Here is more information about interference by the FCC:http://www.fcc.gov/cib/consumerfacts/interference.html