Silent BFG trick
The silent BFG trick is a nasty tactic invented by DeathMatch players who discovered a glitch in Doom's sound code. The trick, when executed correctly, will launch a BFG blast with minimal sound. It involves firing the BFG and using a wall (or jumping), then quickly strafing from behind the wall and letting the BFG ball go. In zdoom this is fixed but if you wish you can turn it on in the compatibility options.
Please note that by enabling the Silent BFG compatibility flag in ZDoom's options menu, you are effectively crippling the sound system - so you may experience other glitches, such as your player's jumping sounds temporarily muting your chainsaw's motor (even if there is no DSJUMP sound present in the WAD file you are playing).