Doesn't IMAC still have anoise score? Should be a slam-dunk 10 if you outfit your engine the way Matt describes. Plus, your servos will all last longer and you will use a lot less battery capacity each flight. Everything lasts longer, and amazingly, you get a little more usable power delivered to the prop. If you think about it, any energy that is not wasted on rattling the airframe and producing acoustic waves from the airframe is going somewhere else - into the prop!