Check by sound

Exploration Stage: Dream Studio
From: Martha
Description: It's surprising that there is no residue of magic in this room... but this is supposed to be a sorcerer's palace. My gut is telling me that something is hidden here. Bring the brass gongs. Let's check out this space.
Completed: Thank you. The sound of these gongs echoes throughout the palace, revealing every trace of magic. The acoustics should be nearly perfect, but the vibrations are completely canceled out and nothing reverberates. Strange...