I'm currently in the process of installing a new head unit and have just about wired everything up. I decided to run a speaker test before buttoning everything up and after turning the lights on, a loud continuous tone was coming from the rear left speaker. I disconnected the connection to the rear left speakers (+ and -) and the tone went away. It's connected just the same as the others using the same kind of wires and it's the only one with the tone. Any thoughts while I still have the car in pieces?