You heard a good amount of rumbling happen in the tomb's central chamber. Those two large statues did look awfully suspicious.
Completion
With your inspection complete, the statues return to their original position. Something seems different in the room, however...
Notes
The warden is jade, standing facing south.
Judging by its color, this must be The Warden.
You see a small indentation where your pawn might fit.
<Place the pawn in the indentation.>
The Warden stretches its arms, then turns hostile! It is a level 46 stone golem with 3838 health. Kill it to "thoroughly investigate" it.
The sentinel is red, standing facing north toward the entrance of the tomb proper.
This red statue looks a lot like the Sentinel's pawn that you hold.
The statue has a small indentation that matches the size of your pawn.
<Place the pawn in the indentation.>
Just like the warden, the sentinel also stretches, then turns hostile. Kill it as well. Once both stone golems have been "investigated", the quest completes automatically.
On complete, a large chest appears at the southern end of the room!