[SOUND / AUDIO] Nexus Tower laser sound effect persists even after there are no enemies in range

While playing on summoners rift, I've heard the nexus tower laser sound effect persist indefinitely during many matches after an enemy first comes in range. That is, while playing the game there is no laser sound effect at first, but if my team's nexus ever comes under attack the laser sound effect starts up when the nexus tower fire begins lancing into enemies (which it's supposed to), but then if we successfully defend and push back all the enemies the nexus towers still emit constant screeching sounds as if they're shooting something when there is nothing there... no enemy minions.... no enemy champions... nothing.