Wheezing, vets say he's fine

Our Maine Coon wheezes a lot, while awake and snore heavily while sleeping. I'd say he's wheezing 50% of the time. You can hear him across the room. We've had him to three vets (including a feline only clinic that is supposed to be very good) and they all say his lungs sound fine. He is 9 months old and has always done this. His sister (litter mate) does not do it. He never coughs or sneezes. Is there something else that could be causing this? 

Hmm, I wonder if there's an issue in his sinuses that's causing the wheezing and snoring? But I would think the vets would have checked?

I'm not sure if this is relevant, but I had a couple of rescues who snored and snorted for a long time after having a respiratory infection as a kitten.  The issue did appear to be in their sinuses.  After reading threads in the health section about how bovine lactoferrin cures leftover snotty noses etc. from URIs, I got some (Amazon, $18 a bottle, tasteless powder in capsules, can be mixes with food). I have only had them on it for about 4 days but the snorting is down by 50% on the two that had a problem.  There's a lot of discussion of it here somewhere.  It certainly wouldn't hurt to try it, it just improves health and the immune system.