So if you follow the G+ community you'll see what I'm having an issue with 60Hz signal traveling through my speakers. This can be a possibility of a ground loop. Ground loop is when a small signal is allowed to travel on what is considered the ground of your power source or audio signal because there's a slight resistance between that ground and the absolute ground that everything is being tied back to.
So in theory with the - of the battery charger being tied to the ground of the power line it could be transmitting a 60Hz signal from the output of the step down transformer and I could be picking that signal up on the - to my amp which is amplified to my speakers, causing an audible hum.
This resistor shows you how the 60Hz pulse could be picked up very slightly, but enough to drive an amplifier crazy.
