[Chas]

This Model 65 is grounded to a dedicated earth ground separate from any ground in the house.

Ideally, that is a good ground, however, it seems to have a higher impedance that a path via the power line bypass caps. So the RF is using the AC line as the ground path as part of the antenna system.

Find an alternate route for the ground, shorter and known to be low or lower impedance.

For snicks & giggles, operated the radio via an isolation transformer, the "antenna" effect of closing a household circuit should go away...

Could, couple a loop to antenna/ground on the radio. Disconnect the ground and antenna connections when operating from a loop.  That "antenna" effect should also go away...

GL

Chas