The noise coming from the 2 turrets of nexus

When you destroy enemys turrets and you go to the 2 turrets of the nexus,if the turret hits you, and then you leave,if you go to the mini map and you plank it to the turrets of nexus you can still hear the noise of the turret like that it is hitting something,but its nothing there to hit like a champion or minion, i think it is a bug, pls fix it :D