Lennon was laying on the back of the couch above my head yesterday, and I noticed that often times when he breathes, there is a slight whistling noise. He is perfectly healthy in every other respect, so I'm not incredibly worried about it, but I could be wrong. Is this something common, or should I worry? We will be going to the vet in a month or so for the boys to get neutered, so I can ask them there then as well.