Do you have other mics to see if it's not something else in the chain?
Could be a bad batch. Any new construction in your area? The analogue end is a bit too sensitive for my tastes. Any new gadgets? Wii remote? Cordless headphones? LED lighting? Roommate who was formerly an alien? As in not of this earth type.
You probably don't want to blow condensed air over the mic. Microns thick is pretty damn thin, err frail. Any environmental concerns like you live in a hut in the sahara and it's 120F in the shade (during winter). Lots of possibilities. But if it used to not do it and now it does it, something changed. MS SP3? Any tube gear in there? Tubes don't last forever, they're called tubes as in short for vacuum tube. At 15lbs per square inch air pressure, it's only a matter of time until a vacuum is not a vacuum. Baring that new Abby roads studio module on the IS addition. (only if)
Lots of new construction in my area, i also added a tube preamp one of those cheap ART tube mp's (i think that's when the problem started) i have since gotten rid of the amp but the problem still persists tried different Mic's its definitely the NT1A. I read someplace else that it may be related to moisture, and that could make sense since from Jan - April my studio was kept relatively warm due to the season. The person said i should store the mic in a warm, dry place for a day or so. Think i will try that.