I've got an old SW-12 that I've had out of service for many years. I'm trying to get it to function properly again. I plug it in and I hear a humming or buzzing sound. It could be a 60HZ sound but the plug that comes with the sub does not have the third ground plug. It is simply a two pronged plug. I hear the noise whenever power is going into the unit. It does not matter if there are any connections made or not. I hear the same noise with it connected to the LFE RCA on the AMP. I hear it when there is nothing connected. The volume of the noise is always the same level whether or not the volume on the sub is all the way up or all the way down or if the volume on the amp is muted or high. When you pass a LFE signal to the sub, it still makes the humm but otherwise functions properly. I get LFE frequencies that sound reasonable and all of the control knobs on the Sub appear to function properly.
Is there anything that I can do to "fix" this noise other than taking it to a repair shop? What might be causing this noise?
If necessary, I could mic the sub and record it and post a .wav file here.