Noise coming from subwoofers and centre channel

Nice detective work, and at least at this point there’s a loop that involves the AVR and/or amp. If it’s me I’d try the simplest thing first that’d be a cheater plug on the AVR, then on the amp, and then on both (if necessary) and see what happens. You could also consider contacting the fine folks at Hegel as they may give you a very quick and effective solution rather than spending time/$ trying different things. I’d be interested to hear what you find.

Okay now, I removed the two HDMI cables on the processor, projector out and Zappiti player in, the noise disappeared completely. I reconnected the center to the external amplifier and there is no noise either. So it’s the video part that causes this problem. First time in 2 decades that this has happened to me...

I’m going to buy two 3 to 2 sockets, it’s not expensive.

I hope it’s not too risky to use such a socket.

I will send an email to Hegel for their opinion. thanks for the advice

Good evening, Nice testing evening!

1-I installed a 3 two 2 pong on the AVR: no change :-(

2- I added another adapter to the Hegel external amplifier: it really doesn't like the socket, very loud buzz :-(

3-I remove the Hegel one and put it on my Madvr Envy processor: I was starting to get discouraged, I put my ears on the central channel and my subwoofers, I still hear a slight buzz and crackling but I would say 70% less loud ... :-)

4- I say to myself, I'm going to add one to my JVC NZ9 to see.... and yes there is NO MORE NOISE!!!!!!!

Does it exist another solution that would have the same result as this electrical outlet? I find it strange to connect a small piece of plastic to a fairly high-end cable. In addition, is this a risk for my projector and processor? Can performance be affected? it is still 2 products worth 45K.....

IFI GND defender?

Thanks again for your good advice, I really appreciate it, thank you all

It is risky to use a cheater plug.  The correct answer here is you want an HDMI isolator, and one way to achieve this isolation is to use HDMI to Ethernet converters...

https://amzn.to/3OyueZU

PS - I did find direct HDMI to optical isolators at around $750 a pair, so the options above are a lot cheaper.

Also, double check you don't also have a coaxial cable coming in somewhere, those are often hum sources, and relatively easy to fix.