Hello. I recently installed speakers and an aftermarket amp for the door subs and speakers. I've recently noticed an annoying high pitched noise coming from the speakers. It's very faint and It sounds like when your ears are ringing. I disconnected the power line going to the amp and noise is still there but a little less audible. I disconnected the radio fuse and noise went away. Could it be the radio ground? Where is that located? I've double checked speaker connections and everything is good. Any help would be appreciated.