OP go read this website.
http://www.repeater-builder.com/tech-info/bonding/amateur-radio-bonding.html It will answer all your questions. You are in a Ground Loop.
There are some professional engineers that take offense at the term "Ground Loop".
If everything is bonded correctly, using shiny metal connections (which I then apply some type of moisture barrier to, even Vaseline would work in some cases) then their can be no "loop".
KD6VXI
Not this PE because he knows better. To believe that completely ignores basic fundamentals and requires you to believe in myths. Myth #2
2.
Wires have low impedance - and, therefore, conducts RF current effectively and efficiently. While understandable, is fundamentally incorrect. Requires you to ignore Ohm's law and the AC impedances of Single-Wire Circuits. To be an effective and efficient circuit conductor requires low impedance. A Single-Wire Circuit only has low impedance at DC and 60-Hz power frequencies. It is physically impossible to use single-wire conductors like grounds for anything other than power frequencies.
Wire of any length or gauge has both DC Resistance and AC Impedance. The resistance and impedance of a wire are directly proportional to its length. The DC resistance of a ten feet length of #12 AWG copper wire is about 0.015 Ohms, making an excellent circuit conductor. At 60-Hz is fractionally higher at 0.02 Ohms, making it a good conductor at 60 Hz.
The inductance of any wire is nearly independent of its diameter (gauge). Inductance is directly proportional to its length and increases with any bends or loops. The same piece of #12 AWG 10-feet of copper wire has an impedance of 30-Ohms at 1 MHz making it unusable as a circuit conductor. Increase the gauge to 750 MCM, the size of your wrist, and the impedance drops slightly to 25 Ohms. At 25 MHz it becomes essentially an open circuit. Apply Ohm's law.
Myth busted.
Fact: All ground wires are for safety and 0-Volt reference point. It is not physically possible for equipment grounds and ground conductors to do anything else. Ground wires are Single-Wire Circuits, where the conductor does not have an equal and opposite associated circuit conductor to cancel out the mutual inductance of both circuit conductors. When two or more circuit conductors coupled closely together form a transmission line. Do not limit your thinking a transmission line is just your coax or ladder line. Audio and telephone circuits use Tip and Ring. Even AC power circuits in your home use a transmission line called a Branch Circuit. For a circuit conductor to be effective and efficient requires impedance to be milli-ohms, not 10's 100's, or 1000's of ohms.