Speaking of G4 sunbathing, I noticed in M1-Engine vacuum levels that you can hear the "switch error" sound when a shot hits a wall. I remember the reaction time being a little different depending on what shot type it was. Punching the wall produces the sound almost immediately, but I think (it's been a while) a trooper grenade produces the sound *before* it actually hits.
I noticed it ages ago, and I dismissed it as monsters in the airlock hallway, then forgot about it. Over the new year I was playing the M1 scenario Phoenix Falling, (which had more vacuum levels than I'd have liked) where the same quirk popped up, then forgot I again. :P