I had a similar problem with a Mavic Open Sport rim on the rear of my '07 Roubaix. As I was cleaning the bike after replacing a cable, I saw cracks around two spoke nipples. On an 11 year old bike, I put it up to lots of miles on the crappy roads around here. I used to weigh 240 lbs, less than 200 now, so that might be part of it. I found a deal on a set of Reynolds Stratus Elite, and replaced the wheelset for $150, on sale. The Mavics were double walled, and I don't know how long the cracks had been there.