I have no idea what caused it to make noises like that, or how it can be reproduced, and I don't really want to try to reproduce it on my own either, it was painfully loud.
I was retaking the mastery rank 9 test with orvius and normal wisp, then all of a sudden I heard a strange noise that sounded like the glaive throw sound effect but stretched out, then followed by extremely loud ringing noise a little after.
below is a video showing the entire mastery test, the bug occur at around 0:47.
(audio warning, lower your volume slider to 1 or 2, seriously.) https://streamable.com/p7a5bp