Noise coming from subwoofers and centre channel

I only use a powerbar...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...

But, your entire system already is at risk as you’ve got no surge protection and there are many here who’ve told tales of losing expensive equipment plugged into the wall.  I have a vey transparent Wiremold power strip, and when I wanted to add power conditioning and surge suppression I just got this and plugged my power strip into it and my whole system was protected on the relative cheap.  I still question if your power strip is plugged in with a 3-prong plug if the cheater plug makes any difference — I don’t know the answer but maybe someone like @erik_squires or someone else does.

https://www.usaudiomart.com/details/650064731-audience-adept-response-ar1p-power-conditioner/

FWIW.

I only use a powerbar...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...

But, your entire system already is at risk as you’ve got no surge protection and there are many here who’ve told tales of losing expensive equipment plugged into the wall. I have a very transparent Wiremold power strip, and when I wanted to add power conditioning and surge protection I just got this and plugged my power strip into it and my whole system was protected on the relative cheap. I still question if your power strip is plugged in with a 3-prong plug if the cheater plug makes any difference — I don’t know the answer but maybe someone like @erik_squires or someone else does.

https://www.usaudiomart.com/details/650064731-audience-adept-response-ar1p-power-conditioner/

I suppose it’s also possible that installing a power conditioner may fix the problem with no cheater plug needed. FWIW.

I’m a huge fan of Furman power conditioners, but I can almost guarantee no conditioner will solve a ground loop problem, no matter how much you spend on it.

Cheater plugs will work, at a high safety risk. What you really want is to isolate the signal ground that causes the loop, not the AC ground.

While there’s nothing in a Furman or megabuck power conditioner that will solve a ground loop, moving all AC plugs to the same strip sometimes is a solution, but it’s not a matter of any circuitry but rather that the grounds are so close.

The OP has already moved everything to the same outlets.  He's pretty much demonstrated that what he needs is an HDMI isolator.

I tried an IFI defender socket this evening, without success, doesn't change anything.
 

All my electronics are on the same circuit, same powerbar.

The Audience Adept arp1 seems interesting at reasonable cost.

I still don’t have an answer that if the power strip is plugged in via a 3-prong plug and the projector is then plugged into the strip with a cheater plug if that’s still an issue.  If the power strip is grounded I don’t see why plugging a component into it with a cheater plug would be a problem as it’s already grounded through the power strip.  Am I missing something here?