Hello @Tonyfromuk, welcome back!
I’m sorry to hear about your experience with your Sonos Beam (Gen 1) playing TV audio after turning off the TV.
This is very weird and I’ve not heard about anything similar to this issue before to be honest.
I recommend you to Submit Diagnostics within 10 minutes of reproducing this and contact our Support Team for some live troubleshooting.
They have tools at their disposal to provide you with information and advice specific to your Sonos system and what it reports.
I hope this helps.
The TV may be powering it’s main board back up for maintenance tasks after you switch it off, without powering the panel.
When you switch the TV off is it while something is playing or tuned into a TV channel or is it on a dashboard which has no sounds?
If tuned into to something/playing when you switch it off it may be resuming when the main board powers up and send audio to the beam, even though the display panel stays unlit.
My own TV performs a maintenance task after XX hours of use and causes my AVR to power on and then power off a few seconds later, due to the TV powering up the hdmi ports as well as usb ports for background maintenance.