Cat makes strange noise when breathing

My kitty is old... And has a hyperthyroid that I am treating but recently he's been making some weird noises. It IS NOT all the time, for some reason it seems like the noise (which is hard to describe... kind of a groaning, heavy, snoring type of noise for a few breaths) happens after he's done meowing at me or if he stands up to walk around. I don't know what it is! I've been searching google and other forums but none of the descriptions I have found seem to match with what's happening. He's behaving totally normal otherwise and doesn't seem in pain or anything. And again, it isn't constant... Only once in a while but seems to be increasing. Any ideas???

My first reaction is that your old guy needs to see the vet.  Although I've never heard this before in my cats, it sounds like it might be a respiratory problem.  The fact that it's increasing is worrisome - better to get this looked at before it gets worse.   Waiting can also lead to increased vet costs.    Please let us know what the vet says.  that it is a minor issue! 

This is true. Thanks, and I will!

The way you described it sounds similar to how I tried to describe a noise my cat was making. I think the problem with my cat is he was puking and either got some caught in his lungs or inhaled water on accident and inhaled that. He also has a multitude of other bad things happening to him right now, which is making him very sick, but if you're in a similar situation with the respiratory stuff, I would try to take him in sooner rather than later, as it did get worse as I waited.