I broke my first spoke a couple months ago, then another a few weeks later. Then yesterday I broke THREE at once. All the broken spokes have been on the drive-side and since I broke the last bunch while track-standing I believe they're breaking due to the back-and-forth forces that none of my freewheeling wheels experience.

Is there a different lacing pattern I can use to prevent this? Would a large-flange hub be better? I've built all my wheels according to Sheldon Brown's instructions and all of them have been fine except for this one. The spokes are all breaking at the head, and in some cases it looks like the head has been sliced in half.

The wheel:
Campy record freewheel hub, small flange
Double butted 2.0/1.6/2.0 stainless spokes
Velocity Aerohead rim, 420g
32x3 lacing pattern
Handbuilt by me
Approximately 10,000 miles on it