i had a similar problem recently, and likewise they all sanpped at the spoke end.
i posted on here and people suggested it was uneven spoke tension as a result of either; a poor build in the first place; or as a result of the wheel being trued too often and twisting spokes / uneven tensioing
i fully slackened off each spoke and fully rebuilt the wheel so the spoke tension was as even as possible.
if you say they are the generator wheels, they would be factory built usually meaning the spokes are super tight when new.
how old are the wheels? are they under warranty? if not then get it rebuilt