Esal, you can't for sure say what is causing the disturbance, but you are fairly confident it's whatever is making all the noise that caused the issue.
Milaki and Claudius, as you advance into the woods, you see that the canopy isn't fully formed overhead and the copse has several areas where you can easily see the sky. The trees themselves do seem to thin out a little bit once you're inside the woods, they are just placed very well to form a "fence" of sorts to stop people seeing into the grove.
As you get about to the end of your 50 foot hike inside Claudius, you suddenly pick up the presence of four distinct creatures' thoughts, though you can't quite detect the surface thoughts themselves yet, not until you focus on one of the creatures in particular.
OOC:
Mechanically, how I'm handling the Detect Thoughts is this:
Because they are currently unseen, you are using the portion of the spell to find unseen creatures. Based on the "once you detect the presence of a creature in this way" portion and the fact that all other features of Detect Thoughts requires you to target a single creature, it will be your next "turn" that you pick a "thought signature" to focus on. It will take your action to use any of the features of the spell, which will prevent you from setting up the trap in that moment. I'm not putting us precisely in intiative yet, but doing a semi-initiative kind of approach until initiative precision is required.
For the purposes of your thought signature stuff, you can target:
Creature A
Creature B
Creature C
Creature D