You may hear feedback from your PC speakers when one or more of the the following conditions are true:
You increase the Microphone Boost option.
The speakers are too close to the microphone.
The speaker volume is turned up so as the microphone hears the speakers.
You have a very sensitive microphone.
You may be able to reduce or eliminate the feedback you are hearing by trying the following steps in Windows 7:
Open Control Panel.
Open the Hardware and Sound setting.
Open the Sound setting.
Select the Recording tab and double-click your microphone you have selected as the default recording device.
Click on the Level tab and reduce the Microphone Boost setting. Note: This setting may not be available for some microphones.
You may also be able to reduce the feedback loop by selecting the Enhancement tab in the microphone's properties page and enabling one of the following options:
Enable Noise Suppression
Enable Acoustic Echo Cancellation
Note: These settings are audio hardware and software specific and may not be available for all microphones.