I just put in a new RCA and my sub now thumps whenever I change radio stations, switch to cd, or turn the stereo off. It has never thumped when the amp turns on as I would expect with "quiet turn-on." Anything in particular I should look at. Thanks

 

Make sure that when you put your new RCA's in you didn't forget to reconnect anything. That sounds like a loose or disconnected ground wire to me.