In Vault:5, after killing the welcoming comittee, I usually go a bit in each direction, trying to pull some monsters from each corner (as well as from the corridors). that way, you should have more time before the random walking from a group of monster gets them to the center. As well, clearing the corridors should help you, as you get more choice for a retreat.
By the way, shouting isn't a really good thing to do there, as it may bring more monsters than expected, with the convokers invoking and the warden blocking the stairs. those aren't really a problem if you go to them : they'll be grouped together, so you can take care of them. Shouting means they'll come from many sides at once, so it will be harder.
EDIT : About the shout. its noise can usually grab the attention of monsters up to 14 squres away. Your field of view is 8 squares, so it's almost twice as much. There is also a thing about "ambient noise" changing it a bit (noise attracting further in Crypt/Tomb, Hall of blades, and Slime pit, but shorter in Lair, Orc, and Shoals).
A scroll of noise is about twice as loud, so it attracts from twice as far. so a scroll of noise in the center of the vault will attract nearly the whole level.
Also, if a monster hear a noise, and is usually a shouter (as orcs, gnolls, but also yaks and many other grouped monsters), they will shout and attract others. It may go recursively, and as there are mostly intelligent monsters in Vault:5, shouting is not the best idea.