I am not a big fan of USB mics or using built in mics.....as the quality is usually poor and problems like this are frequent and usually hard to diagnose and fix. If the mic is OK then it could be your input levels set too high or the wrong default I/O settings on Audacity. You may need to play around with these plus adjust levels to try to cure problem. It could also be "machine noise" coming from your PC that the mic is picking up....try to keep the mic a good distance from your laptop to eliminate this.
Also double check that the version of Audacity you are using is compatible with your laptop bit rate and operating system. There is a section in the Audacity download page that deals with this.