after market radio or stock also are the speakers factory or aftermarket...in either case check the connections on the speaker itself, unplug and re-plug them and see if that worked , also check for any loosr wire strands that could be touching metal on the rear deck, it only takes one wire shard to cause the speaker to make that whining noise, ive had this experience one time and that was because one of my butt connectors had came loose behind the cd player itself and a small piece of wire just happend to be touching a ground point....check both of these spots