There was supposed to be a side quest in Vault 15 whereby you find the source of the rat infestation in Vault 15. Anyone knows how to find it?

The source can be found in the conference room, just north of the room where the SMG is. ( http://strategywiki.org/wiki/Fallout/Vault_15 )

It's not there. I played without any patches, just the clean GOG install. Might be a bug - I examined every corner of that room.

Yeah, the strategy guides were why I even knew there was this quest in the first place. But the only thing I get is a message saying there is a small hole at the corner of the room just big enough for rats to crawl in, and that the rats must have burrowed in.
I then tried to blast every corner and wall with the dynamite you find in the locker next room, but nothing happens. No 200xp, nothing...

Which one is the conference room ? Is it the one with the mountain of rocks in it ?
Btw..ciolan as in..cioLAN ? :D

no u r not doing anything wrong in vault 15 cubicu.
i have also read this in some FAQ's on the net & also tested this extensively ingame.
the 'rat infestation' ends when u have exterminated all 54 rats in Vault 15; it has nothing to do with the conference room tunnel. i got that tunnel message too, but no indication on message window of any 200xp gain as 'Chris Wills' says (his mention of the 200xp is documented in some ppl's FAQs). also checked inside char screen & confirmed no exp is gained. my guess that it is just flavour text, not part of any quest.
or it could be because we r playing fallout 1.1, the last US patch. maybe u only get the 200xp in version 1.2 which is UK patch i think.
if someone here plays 1.2 and can't get the 200xp, i would think that this is just a rumour. just bullshit doesn't exist.