My polk audio psw10 subwoofer has a concent sound coming out of it even if the reciever isnt on or even plugged from it the only way to stop it is to plug it from the wall

The capacitors in the amplification module on the back side of the subwoofer unit (unplug and unscrew amp unit) usually are the second components to check after the fuse. They look like black batteries with white text defining their ratings. It appears to be a commonly under ratted capacity for those that challenge the upper limits of their surround system capacity. (Poor neighbors) These act very much like a battery but quickly build a charge and then release a charge. These can be replaced with higher capacity units that are larger in size and may need to be relocated with extended wires to handle the power demands by the user. They can be ordered online and replaced after discharge and soldered into the proper terminals. The Proper Positive and negative terminals must be followed for proper function when replacing.