Corki W sound effects

Today on patch 6.20 me and my friend both experienced a bug on Corki's E sound effect. Occasionally when the enemy Corki's E activated the sound effect started as normal. However the sound effects of the machine gun started repeating and lasted for almost a minute. This occurred several times during the game. I'm not sure if there are any circumstances that cause the bug, or why it finally stops. I was playing Ivern, my friend was playing Maokai(both of us had smite and we didn't ask if our allys had heard the bug), and the Corki was not using a skin.