Ayesha,
Are you sure you are getting rejected for noise? Don't they usually lump
"noise, artifacting, or pixelation" together for that type of rejection?
In regards to noise, overexposing does seem to work for me. You don't want to overdo it with a subject that has a large dynamic range (very dark and light areas), but I've sometimes overexposed by about 1.5 stops and gotten super noise-free results. Of course, the files have to be worked on to get the exposure levels correct, but it's worth the trouble and definitely easier than trying to get rid of noise.