|You should be able to disable or mute the mic.|
Run Malwarebytes to make sure that you do not have a virus or other malware on your system.
If neither of the above helps, and you never plan on using the built in mic for recording, skype, or other things, consider opening the laptop (or having a professional do it for you) and disconnect the mic's wires. If you are not totally positive, avoid this since it will take work or possibly money to reverse it if you decide you need it later.
You have to be a little bit crazy to keep you from going insane.