I let occassional sounds that I thought were Artemis trying to expell a hairball go on for two years, and it turned out to be asthma (I mentioned it to at least one vet, who told me he had no idea what it was since he hadn't heard it; the next vet I tried was much more helpful).
The best thing to do is to make a vet appointment. The urgency of this depends on the how bad the "hacking" is. One thing that you may be able to do is call your regular vet and get a prescription hair-ball medication without going to the trouble and expense of a full vet visit. That way, if the hair-ball grease doesn't work, your vet will have more information to go on when you do bring that cat in.