If Sinclair steals Bebop ult and kills Bebop, then cancels the cast with spacebar the ult audio plays indefinitely until death or recast of the ult. Even stealing other ults will not stop the audio
Scratch that, it doesn't even have to kill the bebop. It just needs to be channeled long enough. (I found past the B in Hyper Beam is enough but did not check other points)
It occurs right when you kill anyone and cancel the ultimate, it will bug the audio and make it infinite. But yeah currently i can only recreate it with beepbop and dynamo.