The fiero was ahead of it's time and had many engineering firsts incorporated into its design. In addition to your cup holders, the electric motor-driven hvac flap-whacker had been placed our little cars years before it was cool to do so. Before the stone age, and now still, many cars have vacuum operated selectors installed. You are hearing the sound of technological triumph and history.........behind your dash.
OR,
Could just be a squirrel looking for nuts.