Might be a TV glitch, if the TV is fully updated you could try unplugging the optical cable and see if the swapping inputs stops.

If it does adding an inexpensive optical switch so you can connect the Ray to the TV or the empty switch port will end your problem. Usually not good to plug/un-plug audio ports a a lot so the switch is a good idea.

What makes you think the Ray is switching to TV audio - have you tried disabling ‘TV Autoplay’? Also are the rooms ungrouping from the Ray when it happens?

Personally speaking I can’t say I’ve ever seen this issue reported here in the community before. It sounds like it’s a problem with either the cable, or the TV. So if you’re sure about the cause. I would check the cable and maybe give Philips Support a call too. 

Thanx for the answers so far . 
 

the story starts a bit earlier . 
first I had a 37” Philips cineos with bad sound ( broken membranes at speakers ) and then I purchased the Sonos ray.

Being an old television, there was only a coaxial ( electric) digital out. So I bought a converter from coaxial electric to spdif optical . 
already then the ray was switching channels ( from Ethernet/wifi to spdif optical ) with the tv “off” ; standby. 
swapped cables , adapters , everything .. nothing did help . 
At the end I took a converter rca L/R to optical spdif .. powered by tv usb ( which switched on off with the TV. 
That did do the job until recently my new TV arrived , with no rca L/R out :-( 

I started again with spdif optical out -optical in to the ray. Same problem .. ray switches channel with tv on standby.

next thing tried : headphone out => converter to spdif optical => to ray. Same problem .. ray switches channel with tv on standby. 
 

For now I have a work around with a 1 minute delay ( don’t laugh ) . 
The headphone out to optical spdif is USB powered. So I did put the USB power adaptor in a smart plug , and did power the tv over a second smart plug.

By software in the smart plug it measures the power to the tv. When the power is higher than 50 watt ( tv up and running) it powers te signal converter by the second smartplug ) .. giving optical out to ray.. ray switches to optical tv and leave the grouping.

when powering tv off , power below 50 watt… converter switches off. Ray is ready to be grouped by Ethernet / WiFi and STAYS in that structure until the tv is on again . It works with a latency of 1 minute but at least it works.. searching for the proper solution .. 

Maybe? Christmas season TV sales?

A nice OLED set in the biggest size that will fit your space would be nice.

43 “ is an appropriated fit .. don’t care about Oled.. 

Since this happens with different TV’s I’d make a diagnosis after it happens and call Sonos.

Pull the optical cable out of the Ray when the TV’s in standby. If it’s showing red light at the end of the fibre the optical carrier is still active. That’d be why the Ray’s switching to TV.

If the Ray switches to TV some time after the TV’s been put into standby it could simply be waking up for some scheduled activity or other.

Solution? Fully power the TV off at the wall. Use a smart outlet for remote operation. 

Or insert a powered optical switch into the line to the Ray and turn that off instead.

Any arrangement which uses a TV’s analog headphone output through an AD converter is pretty awful. No digital transfer, no Dolby 5.1, etc. Also the signal-to-noise ratio on TV headphone outlets typically isn’t that great.