Listen to this noise...

You may well be right.....my hearing is SHOT but it just does not sound like something firing to me.
When the Box goes bad in this way it sends everything at once, there is no dwell limit its...full blast..and the further the ark, the louder.....so when the revs pick up..it begins hitting a target/ground more, ark shortens to normalish n quiets more as the rpm increases and rotor keeps up

It's a noise you never forget.