Just to clarify,
The big chamber at the end of the descending tunnel had two exiting tunnels splitting off it. The rat chittering one (multiple, multiple rats) and the wet earth and fungal tunnel. Going down the fungal tunnel it split again and you entered the fungal pool one with chittering monster noise but there is still the wet earth smell branch unexplored which had a single faint rat noise that Inamar heard.
The fungal pool room has two narrow animal burrow tunnels leading out of its walls that were used either by the three foot mole creatures or the horse length long but narrow monstrous lithob centipede thing (or both).
I'm not sure which rat room (the rat horde or the wet earth one with a single rat noise) that you are heading towards.