I feel like this is another non-person riddle (which, come to think of it, almost all of the original
Hobbit Riddle Game was, too - personifying the inanimate is pretty much a tradition), but unfortunately my mind keeps jumping to
Star Wars: "Your thoughts betray you."
The repeated reference to voices is pushing me towards someone being betrayed by their own loud voice, but I... don't think Tolkien ever wrote that, so probably not.
hS