Dream of

I'm a small room that's all painted black. At the back of the room on the wall is a small, dim light and to the left of it is a green door. I'm sitting on a chair and in front me is a drummer behind a drum kit and 2 guitarists. Due to the light I can't see their faces but they all look to be the same height and build. After sitting in silence for a while, one of the guitarists starts to play a riff. After the riff is over he stops and the other guitarist plays the exact same thing. No one says anything and after a while it feels like if I can guess what the riff is then I can leave the room, but I always wake up before I can guess it