OP I had the same issue with my dws tires. I had them on my car for about 10k miles and I progressively heard a humming sound more and more. I thought it was a wheel bearing or a suspension related problem but after multiple checks, nothing.
Finally I looked at the tires closely and you could see pretty significant feathering. (Test it by running your hands in the opposite direction of the tire rotation and see if there are "cliffs".)
I notified tire rack and they gave me a full refund towards a set of PSS and I have not had a sound since. I know the dsws were said to be very quiet but I guess I just had a bad set. The car also felt a little squirmish at certain speeds while on its final legs.