Well, I don't know what your past five or six questions were about, so I can't say how good or poor BYC is as a resource for those topics, but there aren't any answers to this one (in less than a day) because I'd be willing to wager that not many people have experienced anything similar. I've worked for a vet for 9 years, and I've gotten to the point where I'm pretty good at guessing with fair accuracy what the diagnosis is likely to be by reading a brief description of the symptoms, usually not any longer or more detailed than what you've posted, before actually seeing the animal. And honestly, I don't know that I could really take a guess at what's going on with your cat.
Nothing about your post screams cancer to me, although cats in my professional experience do seem to be more prone to oral cancers than dogs (probably because they groom themselves more fastidiously and therefor are more likely to ingest carcinogens?). Hairballs don't usually affect the vocal chords in any way, although I guess if he had a particularly violent battle with a hairball he could have damaged his chords somehow. If he's overweight, he could be asthmatic. Although that would only explain the gulping, not necessarily the loss of voice. Allergies and asthma often go hand in hand, and while it seems slightly unlikely that he would suddenly become allergic at the age of seven allergies can develop at any point in an animal's life (for example, I was in my mid twenties before I developed seasonal allergies, and nearly 30 before they were pronounced enough for me to realize that they were actually allergies and not just a "summer cold."). Viral respiratory disease could explain both the gulping and the loss of vocalization. Or maybe he has something stuck in his throat? Something small but irritating like a hair or fragment of grass.
My advice, for whatever it's worth, is to get a licensed veterinarian to examine your cat and see if they can figure out what's going on. Anything anyone here has to suggest is pure hearsay. The notion that he's lost his voice because he was zapped by aliens has about as much weight as anything anyone else here could guess.
