There always going to bang when your turning a bloody great big magnetic coil on and off like that lol.
Still, it gets your body 'back into alignment' (all be it for a fraction of a second!)
Nope...the magnet is on continuously which 'pulls' all your atoms into alignment with the magnetic field; we then blast you with a massive pulse of RF which deflects the atoms slightly out of line with the static field (and creates the noises), at the end of the RF pulse the molecules re-align with the static field at a rate which is characteristic to each molecule and release energy as a weak RF signal as they do so.
Very sensitive RF receiving coils detect the energy released and then it is up to the computers to convert this into an image representing body tissues or a display of molecular types and concentrations within a particular part of the body.