When I turn my car off and the radio shuts off, turning the amp off...a second later the subs make a sound like you are plugging the RCAs into the amp when its powered.
Like you can tell the connection has been turned off, but its an electronic feedback and not an audio output from the cd.
amp gain too high?
Feedback through cables under carpet?
IT never did this until I made a new ground to the metal of the trunk body.