Sion Ult Sound Bug

My friends and I have been experiencing a bug where you can only hear the 'Dong' sound when Sion is in vision. We extensively tested this and it only sounds when he is in vision, if he ult's and never enters vision of your team no one on your team will hear it, however everyone on the Sion's team hears it as they are in vision of sion. We tried this a number of times and the same results happened.