hello there! im just curious if my sub has had a fault as im hearing a small humming sound from the subwoofer. even when my amp is turned off im sure im not hearing things but i cant remember that noise when i first got that system. so what possible causes do you think it is? ive got a standard sub with my AE EVO 3B and my amp is a yamaha RX-V750 from deutsch land any ideas people?