What’s that loud ‘thud’ noise that Jimmy sometimes makes?

There’s his normal footsteps, wood creaking, and then there’s that loud thud he sometimes makes that kinda sounds like if someone jumped into the air and slammed their feet to the ground as hard as they could.

I thought at first that it was the sound of Jimmy closing the stairwell door to change floors but I’ve heard and/or seen him moments after hearing that louder noise a few times now so I don’t think that’s what it is.

Does it indicate a specific action Jimmy’s taking or is it just for variety? Also, is there a distinct sound for when Jimmy changes floors? I haven’t been able to tell so far in my playthrough.