I read sonewhere that the m has the same airbox as the g but that the holes that go to the helmholtz reasonator are plugged and there are no helmholtz reasonators. Would removing these and plugging the holes quiet the car, make it louder, have a negative impact from not being there?

 

Should make it slightly louder, although IDK if it's so much that you would notice. You could also remove the sound-deadening hood liner; that works too. In other forums, there's this thing known as the GAB mod; (look it up). You could do that, too.

All these things are entirely harmless and free to play with. It's your car. Have fun with it.