Anyone know what causes this? It's not a crack and it only shows up when I'm doing a vertical. I asked a few guys at work and only one said he'd seen it before. He thought it was caused by a gap between the pieces but it happens when the pieces are flush as well. I tend to run fairly hot but changing amps/wire speed doesn't make any difference. Current theory is it's the material as it only started when I began a new job. Also the picture makes it look much more obvious than it actually is, it's really just a light, very straight scoring the length of the weld.