There's a dead-end room off of the room with Brakkal, 'Faithful of Maglubiyet'. The dead-end room has three goblins and a rat in it.
If you talk to the rat, it talks about hidden treasure. But I have gone over the room extensively and there isn't anything hidden - no Perception rolls trigger, the Alt key shows nothing, and moving the cursor and camera over the area and the walls shows nothing. I think this is an incomplete or removed lead.
Also, make sure to talk to the goblins with Wyll in the party - the dialog is hilarious (but will start combat).