The houses lack furniture, baggage and leftovers. To compensate the player should see more waste/stuff/useless things in the buildings and cars.
These things should not be able to be picked up. But could spawed in the vicinity of a player like apples under trees.
When a player is going slow throuh this waste, it makes quiet noise. But when a player is looting fast, rushing throuhg the buildings it should make loud noise (attracting nearby infected or players).