Noise coming from subwoofers and centre channel

yes, in fact, there is an unconnected coaxial cable, which was used by a former TV provider several years ago. Do you think there may still be signal even though I haven't been with this provider for years and have never had a ground problem in 10 years?

OP: The coax only matters if it’s plugged into a device in your rack and can create a new ground path. Coaxial ground loop eliminators are cheap and plentiful. Honestly everyone should use them just in case.

Having an antenna or cable TV cable grounded outside your home by a grounding block is code,and not by itself a problem. The problem is when that cable is connected inside to a set top box and that set top box is connected to your stereo. The outer shield in the coax now creates a very long and separate ground path.

By the way, we don’t have the same issues with Ethernet because Ethernet is inherently isolated. Mostly. For this reason we don’t have ground loops when your cable Internet is connected to devices inside via Ethernet.

PS - If the coax isn't used, make sure it's disconnected outside.  Even though there may be no equipment at the provider side that long coax can function as an antenna and bring in lightning surges into the home.  Leave the grounding block in place.

One thought — you didn’t mention if you’re using a power conditioner/surge protector, which I would hope you are given the cost of your system.  If so obviously the conditioner would be plugged into the wall with a 3-prong plug so wondering if then using a cheater plug on the projector is a non issue?  If you’re not using a power conditioner that’s definitely something to address, and depending on how its designed may also help alleviate your noise issue without a cheater plug.  Just some further thoughts FWIW and glad you’ve at least identified the culprit and gotten rid of the noise — that’s gotta be a huge relief!

Hi good afternoon,

I only use a powerbar. Here a link of my model. All my power cable are from Bis audio ( 3prong plug)

BIS Audio PowerBIS Maestro A/C Power Bar + AC20WG A/C Power Cord Review – NOVO Audio and Technology Magazine

Thank you for your findings. Indeed, I am happy to have made the discovery but I do not want to put my system and our security at risk....with the cheater plug...

Not quite sure where you are in your investigation.

If your system is connected to cable tv I will share I had a pretty obvious hum/buzz. 

What solved my problem entirely was connecting the following Jensen VRD-1FF IsoMax CATV Digital RF Isolator between my xfinity coax and the xfinity cable box needed to run my TV.

Jensen Iso-Max VRD-1FF 75 Ohm Inline Digital CATV Isolator Hum Eliminator (parts-express.com)

Note that the coax from outside is first split and one leg goes to the TV and the other to my modem/router.  This was only needed on the coax leg going to the xfinity cable box.