Sony Active Subwoofer noise. Subwoofer suddenly makes loud buzzing sound when system is off, and

Question

Subwoofer suddenly makes loud buzzing sound when system is off, and air blows through hole in bottom of sub. Noise goes away when turned off. It comes back later for ** reason. Sub works fine when whole system is in use. I tried unplugging power supply form sub and receiver in hopes of resetting sub, ** luck. Is it the sub or something else.