I'm on one of the later levels, the one where I'm in the train with my team. the door opens, we snipe the towers, then I head into the room, and find a door that won't open. Msg says "Hint. Use the wheel to open the door"

Where's the wheel?
I can't find it!

you go up to the door, look to your right- then down. i think it even glows RED.