There is a reason why a great many things are called fixtures: such things are meant to be securely fixed, attached, usually to a surface. Whereas a loose fixture refers to the state of that object, the play is rather possibly the range of motion available to the object in that state:
- Movement or space for movement, as of mechanical parts.
That state and the space for movement are conditions where noise may occur when a force sets the object in motion. So if someone comments about hearing a rattle in the wind, couldn't they say that "something is(the fixtures are) playing in the wind", with no reference to music or an animal running around or what not? Could they say that there's a play with some fixtures or do the more casual meanings of play completely upstage the motion sense here? Is "(the sound of) a loose fixture in the wind" the better way to express this; would that be confused with a *fixture (set/let) loose in the wind*, as in completely free from any restraint and not just sort of "hanging"?