What sort of noise are you hearing? Is it consistent? Is the snake sneezing, gaping its mouth open, or showing other signs of infection?
If the noisy breathing is actually caused by an upper respiratory infection (URI), there are several things you can do to help the snake. Make sure the viv is as dry as possible; no humid hides and a very small water dish, washed out 2X daily. Increase temperatures to the upper 80's F, nearly 90. Be SURE that the snake has a way to get away from temps that are too high, though. This isn't a recommendation to avoid a vet visit, but sometimes a dry environment and a temperature boost are all that an animal needs to recover. URIs do need to be taken seriously, as snakes have only one full-size, working lung and can get very ill very fast from respiratory issues.
Yes, URIs are often contagious. Handle the affected animal last, and wash your hands and arms thoroughly to minimize any cross contamination. If you can, I'd actually move the healthy one's viv to another place just to be safe. You don't want to cause any more stress to the sick one, and moving is stressful for territorial animals.
Hope things improve soon. Let us know how things go.