i am getting a buzzing sound from my frontspeakers

Please help. I have had my home theater/music setup for about six or seven months in my new home. I have never had a problem with buzzing before, except a light buzz in my rear speakers, which was hardly noticeable. Today the front ones started buzzing really loudly when my amp is on. It disappears when the amp is turned off. The only thing I did different was to switch the front left and right connection at the preamp today because I realized I connected them wrong when I changed interconnects a couple of weeks ago. I did not turn the amp off when I disconnected the cables today. Could this cause any damage and be the reason for the humming? I know all manufacturers recommend turing everything off before connecting or disconnecting anything. I also blew a fuse a couple of days ago in the room but I don't think this had anything to do with it. Am I going to have to send in my preamp or amp for repair or will this go away? Thanks for your advice.