I have a JBL Bass16 subwoofer that was part of a HTIB and that I have owned for 14 years. This system had been setup the same way in the same location in my basement for all that time. Over the past 4-5 months I noticed that my subwoofer was making a humming noise. It was not that loud but I noticed it and I never noticed it before. One day I noticed that my front speakers and subwoofer were connected to the front (A) and (B) terminals on my receiver. My sub has no LFE input jack so we have to connect it to the terminals for the front left and right speakers on the receiver with speaker wire. The actual front left and right speakers are connected to the other set of front speaker terminals. I wondered if this was the best setup so I did some research and realized that it was better to connect the front L/R speakers to the speaker output terminals on the subwoofer and then connect the sub inputs to the front L/R outputs on the receiver. When I did this, the sound coming out of the front L/R speakers became much more muffled when I played anything out of them. I also noticed a subtle buzzing noise coming out of the front L/R speakers that I hadn't noticed before. When I turned the gain on the subwoofer all the way down, the speakers didn't really sound muffled anymore but as soon as I turned that gain knob on the subwoofer up even a little bit the muffled noise came back and it got louder as I turned the gain on the subwoofer up. After doing this I connected my front speakers to the receiver like they were before and I had normal sound again. My point in telling you all this is that not only is there a humming noise but for some reason, connecting my front L/R speakers to the subwoofer made them sound muffled when that shouldn't have been the case.
Today I was trying to figure what was causing the noise. First, I unplugged the subwoofer from my surge protector and then plugged it into an outlet that was away from the surge protector. The noise was still there. Next, I pulled out the speaker wire that was connecting my subwoofer to my receiver, unplugged the sub and moved it to the opposite side of the room where there were more outlets and where nothing was connected to the sub. I tried plugging the sub into two different outlets on the other side of the room where there are no electronics nearby and the humming noise remained. All my outlets are 3-prong outlets and the plug on my subwoofer is a 2-prong plug. This doesn't seem to be a ground loop problem or a problem with one of my outlets based on what I did. The other thing I want to note is that when the subwoofer is turned on, the buzzing noise becomes worse the more I turn the volume knob down. That is strange to me as I would have expected the opposite.
Does anyone have any suggestions as to what this could be and what could be done? Should I stop using my subwoofer? The last thing I want to note is that my sub is at least still producing bass when watching movies and playing games and it doesn't sound distorted or anything.