My Roku box started screeching, popping and distorting the screen and then shut itself off and came back on by itself. I have restarted and reset it and changed to a different HDMI port to try to solve it but to no avail. I guess it needs to be exchanged for a new one but there is no way to get in touch with a live person
If it's still under warranty try:
Step by step instructions for returns and warranty replacements | Official Roku Support