[cpollock]

Just a thought, the dipole antenna is sensitive to electrostatic noise, which is pretty common from anything that sparks. If you use a loop antenna, as when you attached the other end of your antenna wire to the ground terminal, both ends of the wire see the same electrostatic noise, so most electrostatic noise cancels.
Loop antennas respond to the magnetic field of the RF wave. Magnetic fields are created by currents, which are less common in natural sources, so there is generally less magnetic noise in the environment.
The challenge with the loop is that ideally it has a circumference almost equal to the wavelength, so it is not very practical for AM bands. Some of the Philco models incorporated multiturm loop antennas in the cabinet that were impedance matched through the input coil to provide optimal signal.
There are other ways to make small loop antennas ( see makearadio.com/loops/index.php for a few ideas). I'm just putting one together based on this site, and will fill you in if it works.