It must be hilarious to watch the aliens attack every possible sound like idiots

They don't attack every sound. That would have them running endlessly in circles. For example the sound of rushing water they recognize as natural and non food related. I assume they learn to ignore the sound of birds since being unable to fly, they probably can't catch them - at least not often enough to be worth charging toward every birdsong.

I'd imagine creatures like these would be very tuned in to a series of noises moving between points A and B (the signature of a living thing) or clearly artificial sounds like metal clanking against metal or music. Single incident noises like falling acorns or tree branches wouldn't elicit a response. So if you happen to step on something that makes a noise, but freeze in place and don't move for a while, you'd probably be safe. One crunch is okay. Crunch, crunch, crunch brings the monsters. Assuming any of them are around. If they're all far away at the moment you could probably make louder noises and not have to worry. Trouble is, how would you know? You always have to act like there's an alien close by - because there might be.