So a while back I broke a spoke on my mtb, I replaced it and it seemed like no big deal. However, since then every 3 or four rides I get a broken spoke. I initially thought that maybe I didn't know what I was doing and took it to a shop and had them replace the spoke and true the wheel. The result is the same (broken spokes).

The spokes are breaking right at the nipple which means I've been having to junk them. I've also that they seem to be on the non-drive side with the disc brake. Finally, the rim has faint, small lines (possibly stress lines?) that run perpendicular to the edge of the rim. I showed these to a mechanic and he said to monitor them but not to worry too much.

I've heard some people suggest that when this happens you should think about rebuilding the wheel? Is this just a tensioning issue or is this something that I'm going to have to replace? It's putting a real hamper on my ability to go ride.