I did a runthrough to Throne Room (S) and encountered some of these in Castle Zvahl Keep (S), on the way up. I had two of them aggro me, and I'm about 80% sure I had both Sneak and Invis up at the time, so it's possible the ones in this zone are True-Sound.
Another thing I found odd, I had both of them attacking me and whilst one started casting Blizzard IV the second Doom Lens just stopped, stood idly by and did nothing at all. Didn't cast, didn't move, didn't attack me - even though it was around two steps away and facing me. It fell back into its idle animation pose, but upon running away down a passageway, it followed me along with the second Doom Lens. They do de-aggro quickly under the effect of Gravity and Bind when you run away from them, but this wasn't the case with these above - they were literally on top of me when one of them went idle. -- Orubicon 13:17, March 24, 2010 (UTC)