It's because Satan wants you to think it's weird! Sorry, I couldn't resist. People used to look for hidden satanic messages in songs playing records backwards. It does sound like the air is being sucked in. But, I'd be interested to see what information people have on this, because in a lot of languages air doesn't come out of the mouth when making certain sounds. Even the same or similar consonants in various languages are pronounced with air escaping the mouth or none at all.

So you might want to look for a type of sound called an implosive, they're uncommon but not really rare in natural languages and when they are used there are pretty much always more plosives than implosives. An easy theory on why could just be that they disrupt your breathing pattern, we pretty much always breathe out but in takes extra effort. Not a scientist thought, just a conlanger so dont take my opinio seriously. Wish you the best of luck in your explorations!