Speaker humming.

[Swede.]

Hi y'all!
Been researching this both on here, online and tested a bunch at home (off course), to no avail.
So here goes.
Been having hum in speakers on a 5.1 system (house have wiring in walls, not done by myself) and its been really inconsistent, some days really loud, so you hear it even watching a movie, other days really mild. Found my subwoofer didn't put out power well all the time so pulled that thinking maybe that failing internal amp messed with it all. Nope. But better.
The main unit is a Pioneer 'Elite VSX-31' amp. These don't have any ground wiring in the power cord from factory, so ground loops shouldn't be a thing, right? I've checked the outlet so it's wired correctly, and it is.
Pulled an extension cord across the room to another, unused outlet that's is on another breaker from amp/PS3 (on separate outlet but same breaker) as the TV and LED light behind the TV (IKEA sling) Same noise...
BUT, when removed the subwoofer the wires behind was visible and looked bad, so I bundled them up some and tucked them away a bit, AND now it's much less humming than before..!
WTF!?
Could it be interference/dirty power and the 'coils' in the power cords working as a filter?

 

[lovinthehd]

Your tv could tv/cable could still be connected electrically to your avr for ground loops. How about that light? I might try disconnecting that. Could be something to do with what cables you moved/affected, hard to know. Could be items elsewhere in the house like dimmer switches, motors, etc causing the variations in level.

 

[Swede.]

I only use an HDMI from reciver to wall connection that pops out behind the TV with another HDMI there. Use a 'Chromecast' for all streaming and occasionally the PS3 for BluRay/DVD (also hardwire with HDMI) Have tried unplug all and it still hummed, till the bundling of power cable like described.
Might try to coil it better and see I that kills it completely.

 

[Cos]

If you haven't already tried this, unplug all HDMI sources from your amp, and see if the hum is still present.

When I was in my older townhouse, if I had my Comcast(cable) provider connected to my equipment, I would get humming in my speakers. If that is the case, there is a very simple solution in purchasing a cable isolator transformer by Jensen.

Jensen Transformers VRD-1FF ISO-MAX Cable TV Ground Isolator (cs1.net)

There is another brand I have used, but I can't seem to find the model number. Some cable & Satellite companies can introduce ground loop hum into your systems.