Not sure about the monitor speakers. You may try using TRS balanced cables.
The noise you describe and fairly specific circumstance that causes it, sounds like what we like to call... "Feedback". The mic is picking up what the headphones are putting out. It loops and loops and builds and builds until you get a sound that would even make Optimus Prime proud.
Turn your input and headphone level down a bit. You might also try using headphones with more isolation.
The mic you use may also have an impedance switch. Try adjusting this to a more comfortable degree.