This might give some clues, but no real answer to manufacturer. From the website
http://www.climbonline.org/news/recalls.shtml:
"January 8, 2006
Widespread Spoke Failures
Bike shops are being forced to build hundreds of replacement wheels each week because spokes in stock wheels are failing. The problem is currently found in bikes costing up to $600 from makers such as Fuji, Giant, Jamis, Pacific Cycle, Raleigh, Specialized, Trek and others.
The scope of the problem is still uncertain, according to a cover story in the trade magazine, Bicycle Retailer & Industry News. Bikes made for the above companies in various Chinese assembly plants received wheels laced with defective spokes.
The spokes are breaking in the middle and/or rusting. It's suspected that cost-cutting by a Korean company resulted in substandard wire being supplied to spoke manufacturers. According to the magazine, tests show that the spokes have nickel and molybdenum contents far below normal levels.
The faulty spokes may have N, Z or S stamped into the round head or no insignia at all. If you have a 2004 or '05 bike in which the spokes begin rusting or breaking, check with the shop where you bought it."