I usually do the introductions a bit differently. The new cat has its own room at first, so I let one old cat in that room at a time. (while I am there) I try not to interfere, but I will talk and sometimes pet, both cats. The level of noise will depend on the cats. But it is possible that if one old cat is threatened by the new cat he may take it out on a cat he already knows. But try not to worry about that. They'll get over it. Then I'll try it with another cat, and so on. I usually do not give them the run of the house until they are at ease with at least a few of the old cats. (don't want a cat fight while I am not home). I have been fortunate enough to have instant friendliness, but the norm is usually a few weeks. BUT, Thumper, the 3rd cat I took in, took 1 YEAR! to adjust. But in the end, he was with me for 12 years, and he liked his room mates.