Had same bug in multiple matches yesterday playing as Bebop myself. This seemed to occur, more often than not, when the Beam Special ability action is canceled manually, or interrupted. I also noticed a considerable frame drop when this occurs. during a match yesterday, I had 3-4 of these sound effects compounded on top of one another; the sound became so unbearable that I simply took off my headphones for the remainder of the match, there were multiple lag spikes that multiple others also experienced during said match as well (I didn't log the Match ID at the time, though I could look it up if given instruction on how to do so).
Coming from a coding background, I personally believe the issue to possibly be something to do with the sound effects of the action either being stuck within a loop, or similarly, not being terminated completely (during plasma beam action interruption). I lean more toward the first, as this issue seems to also cause increasingly serious lag spikes with the amount of stacked sound effects, which could be linked to a memory leak.