Uneven spoke tension sounds like a reasonable idea.
If the wheel is 2 years old, how much have you used it? I take it, from the spec it's for MTB, and the rim is fairly heavy duty, indicating that it is designed for hard All Mountain use, has it just had a hard life of impacts; and the wheel is comming to the end of it's life?
As for the rim / hub being high end, this does not have much if anything to do with the quality of the wheel build.