Anyone know where to find the hidden shiny the rat in the shattered sanctum talks about?

[Senkoau]

I found a rat near the goblin prisoner inside the shattered sanctum and its talking about light and shiny's below the floor but I've been all over the rooms near it and moved the boxes and crates. I can't find what its talking about. Anyone know where to find the shiny its referring to?

[Anima Mundi]

I'm pretty sure it places a marker on your map right on the spot after talking to the rat if you convinced him you're friend.

The "treasure" (it's really nothing great) is hidden in a loose stone (which i believe your char needs to pass perception check to highlight)

[Senkoau]

I'll take a look on the map when I next play, not sure if I convinced it to be my friend I was using animal speaking. Thanks.