Just listen to whatever surrounds you. Sound is a good object of meditation because we generally do not try to control it as much as we do other things. People often have a more difficult time settling into their bodies than they do paying attention to the sounds that appear naturally. Just listen and try to let whatever sounds are around you pass through you.

The fundamental purpose of meditation is not to create a comfortable hiding place for oneself; it is to acquaint the mind, one a moment-to-moment basis, with impermanence….When the mind is settled, the underlying ephemeral nature of things can be more clearly perceived. Resistance diminishes, the flight to past and future recedes, and the sense that it might be possible to respond consciously rather than react blindly to events begins to emerge.

Mark Epstein,  Advice not Given: A Guide to Getting Over Yourself