What shutter speeds were you using? I know the noise gets worse with time, but not sure what the threshold is.
conductor- 400 iso, f/2.0, 1/180
dancers - 400 iso, f/2.0, 1/180
single dancer - 400 iso, f/2.0, 1/180
camera man - 400 iso, f/2.0, 1/45
single man - 800 iso, f/2.8, 1/350
singer w/ group - 800 iso, f/3.5, 1/350
entire group - 400 iso, f/2.0, 1/500