Can anybody explain this?

It’s an echo

It’s not a crazy phenomenon. It’s an echo. You can find places in cities where you will get this sound as the noise bounces off buildings

O wow... this can be recreated most anywhere There is a corrugated metal surface. There is nothing special about this.

What’s the big deal it’s an echo

The sound pitches down, which means it’s moving slower. Each post or stair creates a reflection of sound. So if there are 200 reflections, each one is pitched down lower than the previous one. If each reflection is only 20 milliseconds apart, then what you hear is a smooth pitch down like a laser gun. The closer posts come back close to the higher original pitch. The further posts take longer to come back, so it’ll be lower pitched. This ain’t rocket science y’all. It’s similar to the Doppler effect but coming off a reflection.

I should call her

It's called clapping, I've heard of it

Simple the clap echos of each stair, which is a little further, creates a Doppler effect on the sound. Same with the wall and the fact each slat is offset from the one before it

I have no idea what is going on

Dopler effect. Because it is not a single flat surface but multiple small, flat, parallel surfaces at slightly different distances, the sound is returned (echo) at slightly different time and frequency. The echo sounds like a chirp rether than a clap. Its pretty cool.