First off, I'm pretty sure it isn't the mic. It is some kind of distortion, like the gain is set to high. Use the back headphone/mic jacks instead of the fronts. If you're using the back ports and still getting the distortion, you might want to check the windows and sound chip settings and adjust as needed(not sure what mobo you're using). The sound chip could be realtek or others, but they work pretty much the same.
Also, it could be the onboard sound isn't good. Usually, onboard sound doesn't have many problems. Or you could be getting some inference from the computer itself.
Try the things suggested and get back to us with more info, like model of mobo(or laptop) and model of the headsets.
Happy distortion free listening, the Prisoner...