The switch contacts are actually arcing inside, making the noises that you are hearing. This can lead to burn contacts and heating of the switch and wiring connected to it. This in turn can lead to an electrical fire if the issue isn't addressed. Changing a switch isn't hard to accomplish. In fact, in my article How To Change a Switch, I show you step-by-step instructions.
In order to determine if a switch is defective, here's an article that tells you what to look for in determining a defective switch.