Now you know my pain

The grounds are good.  What else could be making that noise?  Is it the treble bleed?  That's the only thing that's not present in the 540RHH and the N4.  It's a pretty standard 330 pF cap with a 100 K resister in parallel, connected in the usual way across the volume pot's middle and left lugs (if you're looking at it from the bottom of the pot and the lugs facing downward).