Some TV's do not have an ajustment possibility of the level of volume for their optical out. Which results in increased sonos volume during watching television. When switching back to internet radio or spotify a sudden volume increase will occur throughout all sonos systems which are groupped (because the master volume has been increased in order to compensate the low optical-out volume level of the TV). A volume level change option of the optical-in on PLAYBAR i.o. to compensate would probably solve the issue (see PLAYBAR as a sort of a "pre amp" for putting your TV sound on the Sonos network (frequently used when viewing concerts)).