sounds like you solved your problem bpf.But before building one,
why dont you put the rig in some shielding and build an inline filter before the rig?maybe install some caps to ground?
maybe .o1 uf ceramics to ground? i have built mine today and it receives fine. took it mobiling with me i dont have this problem.But they probably dont run the freqs yours does.
I physically connected a ground wire to the case of my radio and hooked it up to the nearest ground connection which at home is the 8 ft triad ground rods i have driven into the dirt for other equipment.Not only do i have an antenna ground i have an earth ground too to the case of the radio.it really reduced the noise in my receiver..
I started out with an old johnson viking tube rig with an s38b receiver. :). I ground everything including my wife from my bank account hi hi. one wire with a ring connector or fork if you dont have the ring. or rap the ground wire around the screw and tighten. see if that helps.