There is no sound because there is no relevant audio and we probably don't enjoy the same music.
As part of an internal game jam here at the office I modified my SMKCycle (an exercise bike I retrofitted using Arduino to play Super Mario Kart on my SNES) to interface with unity and a colleague, Mike McGraw, made a 3-D game designed around the bike.
The Game Jam had a 1 week time frame and all work was done on evenings/weekends. I must admit that my contribution (the bike modifications) was probably significantly smaller than Mike's (the game) but everything ended up pretty well.
The game itself puts the rider in the position of defending the town/himself from rampaging alien oranges (The game jam had specific themes). There are 2 modes the bike can be in, a travel mode where peddling moves you forward at a relative speed and the left/right buttons turn left and right. Once you are in a position to fire on the vile citrus you can press the center button and switch to gun mode. In gun mode the tank stops and begins shooting (the rate of fire is commensurate to the speed at which you peddle) and left/right again turns left and right. At any time you can press the center button to swap between the different modes.
Thanks again to Mike McGraw for being interested in the project enough to dedicate some real time to it.