Lessers have been known to have subtle deformities that can cause this. I would not have been surprised at all if this was a cinnamon either. For lessers in super form, they can have 'bug eyes' which is basically a compressed skull where the eyes will be pushed out and look larger than an average ball. This compression can also impact the nasal passages and make irregular sounds when they breathe. For cinnamons and super cinnamons, they have 'duck bill' which is a similar issue but further up on the snout - short/flat nose. This is much more common to cause breathing sounds (I've had 2 cinnamons that whistle subtley since birth). Shedding is another cause of this.
Just keep an eye on them. As long as you don't see any mucous around the nostrils or mouth and behavior doesn't change dramatically you don't have to worry.