I have a Roku Premiere. Had it for about a year. In the last day or two the audio has become extremely muffled. Sounds like the speakers are smothered in pillows. I have switched HDMI ports and cables, checked the audio settings on both the Roku and TV and rebooted the little Roku box 2 or 3 times. No luck. The TV's sound output is pumped thru a stereo amp (Visio TV, Onkyo amp). When playing a DVD which uses the same sound setup there are no fidelity problems. So the problem does seem to reside in the Roku box.
All streaming services that I've checked (YouTube, Hulu, PBS, Netflix and Amazon) have the same problem. What's odd is the little clicks and beeps coming from the Roku box when navigating around are in their usual high fidelity. Also advertisements on YouTube are much louder and the fidelity is better than the content being streamed.
I'm about out of ideas here, so I'm posting this as a last resort. If this doesn't clear itself up (sometimes the box will do that after a reboot, though not this time) I'm just going to get an Amazon whatsit equivalent. The Roku has been great until recently, but if I can't get this fixed in the next day or two I'll switch to something else.