Iv just had exactly the same issue.... right down to the tone pot cancelling the buzz!
I swapped the pots, the cap, the jack, the pup, the wires... all to no avail.
I heard that cheaper jack sockets sometimes suffer from a bad earth between the inner ring and the lug (they sometimes dont get crimped together properly). Did the 2 jacks come from the same batch?
As another idea, are all your grounds from the same point eg the back of the pot? It is possible to create a ground loop which could give you some buzz....
As of yet I havnt been able to resolve my issue, but have some good quality pots and jacks on order, so Il let you know the outcome.