1. are you really carrying both a medium machine gun and a carbine? that seems not to be the best way of working, but I have no idea what is SOP where you are. we usually had the machine gunners just carrying a maching gun and a handgun, or a knife (and I would say this is one example when a knife is a good back up weapon).
2. why are you clearing rooms with a medium machine gun? wouldn't it be a better idea to have you providing squad/platoon security? its hard enough to clear rooms with a carbine, a machine gun is not the right weapon, IMO.
3. a machine gunner has less reason, than anybody else, to be all alone in a room with a bag guy. if that is the case, sure, maybe your knife if what you need to survive. but I am not saying that a knife is not a good weapon - I am saying it is a waste of training time. what is the chance that you will be faced with knife welding enemy when you are alone and your firearms are all inoperative?