Hi Your amp is probably full of dust. Remove the cover (with the power off of course)and use a vacuum cleaner to remove dust. DO NOT touch any components!check the fan at the back and clean it thorouly, make sure its connector is properly seated. Once you are happy everything is clean, reasemble. Connect all cables and check before powering up. set volume to low, insert cd or similar start playback. Look at fan at back of case it should be off, turn up the volume and the fan should start, increasing speed with increased volume. If the hum on the sound is still present your amp may need to be repaired, take to a professionanal.