Please see the thread linked in this ticket. I have also updated it with new information.

"Hi guys, thanks for your input, anything helps ;)

I've been continuing with this and made an interesting discovery. I thought I'd try lowering Arma 3's volume in windows volume mixer to a fairly low value like 5 (from where it is normally at 30) and then adjust for the decrease in volume in Arma's sound options. Now, I could reproduce this issue pretty much consistently just starting the game, going into the editor and lobbing a few grenades which would give off really amplified explosion sounds and some that weren't. But with this little volume adjustment it at least seems to stop that from happening.

I can only hazard at a guess that the volume setting in windows is conflicting with Arma 3's and perhaps is causing sounds to 'double' (or something like that) in volume."

Added another possibly related ticket #0001145.

Added another video demonstrating the problem.
Also added my PC specs.