I have a simple Trotronics sound bar. It plugs into the TV with an optical cable. It worked just fine with my Roku Premiere. Yesterday I switched to a Roku Ultra. When I turn on the soundbar since connecting the Ultra, all I get from the soundbar is a loud, continuous, horrible noise. I don’t understand how changing the Roku would affect the soundbar. Does anyone have any ideas?
Try changing the settings under Settings->Audio. There may also be TV settings that affect what comes out of the optical port.