AirPods usually chirp as a status alert; it’s Apple’s way of telling you something without using your phone. Most commonly, it happens when the battery is low, when you place them in the case, switch between devices, or when Find My is active (like a location ping or separation alert). I’ve noticed mine also make a quick chirp if there’s a connection hiccup or after a reset. If it’s happening randomly, it’s worth checking battery levels and the Find My settings, since those are the usual triggers.