First, housing together is a bad idea. They will be competitive for everything. The only time they should be together is for breeding and even that is moderated (3 on 3 off).

Define sound...?
Wheezing, hissing, gurgling, sneezing, whistling....ect?
In most cases if something has changed in their behavior and they start making funny noises you should take them to the vet for a check.