My TV model is a 55pfl8007K and I have already changed it once for this problem without success:

When an HDMI source (I tried with multiple sources including a popcorn hour, a raspberry pi, and a freebox) is connected to the TV and I use the optical output to send the sound to my home cinema, I can hear a strange, somehow repetitive and acute noise in my home cinema. It looks like I'm hearing the TV's internals working but this is hard to describe. This happens even if no sound is generated from the HDMI source and it tends to amplify as the TV warms up. I can't hear that from the TV speakers and under the exact same conditions, this didn't happen with my previous Samsung TV.

I tried replacing my HDMI and optical cables without any success. I was told this was an incompatibility between the TV and my home cinema but I have no way to check that except buy another home cinema and possibly have the same problem

When I plug the optical cable right out of the HDMI devise, I can correctly hear the sound, this happens only if it goes through the TV.

My specs:
- TV: 55pfl8007K
- Home cinema: Pioneer