Why do mic cords make noise?

Two of my mic cords make noise, as if you are tapping on the microphone, when you touch them anywhere along the length of the cord.

Is there a problem I can fix, or just toss them and replace them?

The mic cords make noise when you touch them probably because they are poorly insulated and when you touch them a small (unnoticable) amount of current leaks throught the insulation and into your body... interupting the signal of the mic. If it's a huge problem I would recommend getting some high dollar mic cables. If it's not that big of a deal and you were just curious... I wouldn't worry about it. Just avoid touching them.