What Jim said, plus have you turned on the central heating recently? When a guitar starts to buzz it can be a sign of low humidity < 30/35%. Have you changed the string gauge? If you go too light you can get buzzes, too.
+1 to what both Jim and John have said. I had a similar problem last winter on my Collings, took it to someone, who diagnosed winter/central heating related humidity as a problem. Started using a simple Planet Waves humidifier and upped the string gauge from 11s to 12s - problem solved
Thanks for you input. I haven't seen a tech guy to get setup yet but it'd be good to have an idea or two of possible causes for the buzzing sound. It seems it's the 1st, 3rd and 6th that's got the buzz. Will report back after I make the trip to my good friend who fixes my woes.