It's a basic fact of life that whatever you are doing there will be somebody who will ignore you or even forget that you're there and there will always be someone who will get up and walk out, for whatever reason. The performer will just get on with it. On the other hand if they all get up and walk out!!! As for some noise in the audience, ignore it, a bit like the gymnast doing a back somersault on a piece of wood 4ins wide and everybody cheering the person doing the same thing on the floor to the strains of some classic music!