This sound, which I can't say I've ever encountered, seems wayyyyy more dangerous.,(reply>), @Captain Quirk it's a totally flat sound, it's not really a hiss.,(reply>), @Captain Quirk Have you heard it IRL though? It doesn't sound like that at all.,(reply>), Nah in my experience (in Australia) it's very noticeable.,(reply>), @Michael Abbott : That's the problem.  This hissing sound just sounds like any old construction noise -- not a truck backing up.,(reply>), You probably have and don't remember it. It's like a smell you can't describe or remember until you smell it again. Whenever you can hear that noise it's around construction equipment, so when you hear it your brain goes "there's construction equipment nearby, better be careful"