Rhythmic banging near oncrete Forest, Cant find source

[StickChimp]

I was exploring around concrete forest, near where you pick up decider and there's a banging noise in between Hell, Concrete Forest, and Cement Factory.. I cant find whats making it..? any ideas...?

[arghy]

Did you explore underground? i just walked past that and opened the door but didn't go down the ladder. I was worried it might be a future quest so i've been holding off on merc'ing every new location since i've apparently done this a few times already haha.

[arghy]

Theres a ball lightening anomaly underground that explodes at the end of its route--i think that's whats causing it as it gets really ♥♥♥♥♥♥♥ loud.

[Mr_Purple]

That's a burer and poltergeist in the explorable bunker underneath. There are two entrances