I very strongly suspect what you are hearing is feedback. This is caused by the fact that your microphone is picking up any and all sounds reasonably close to it, passing those sounds to your computer and then to your speakers, which transmits the sounds which the mic then picks up and passes to your computer, etc., etc. The resulting sound very rapidly becomes very loud and potentially damaging to your speakers, not to mention your ears!

The solution is simple in concept but, depending on the set up of your computer, may be slightly harder to implement: you need to ensure your speakers are turned OFF when using the microphone. If you need to hear the sound of your voice and/or you need to synchronise your voice with other sounds, you will need to use headphones rather than your speakers, at least at any time the mic is "live" (turned on).

Jeff