I've done a RAT test on a Bombardier Global Express. I have no idea what it sounded like outside, but inside it sounded like a propeller aircraft. The cabin is normally very quiet (good sound insulation) but with the RAT deployed it was almost as loud as flying a light single. I imagine that outside the aircraft it made a helluva noise.
I can't see any reason to do circuits with the RAT out. It's there to provide hydraulic and electrical power if all four generators go offline or all three hydraulic systems fail. It's the very last chance to get you home. If you've landed with the RAT out you're not going to take off in that plane for a good few weeks!
With any luck, below there should be a photo of the RAT
