Have you tried plugging in your device into another HDMI port to see if you are still experiencing the issue? We would also recommend trying to plug in the device to another TV to see if you are seeing the same issue.
I am having the same problem. I have 2 roku express and the problem only seems to be with one of them. I tried switching the devices and am still only having problems with the one. I find if I unplug the skinny plug from the device, if only momentarily, the flickering stops and I get a clear picture. Is the problem with my Roku or the outlet it's plugged into. Please advise. thanks.
Have you also tried switching out the HDMI cord used to connect the device?
If you are still having issues with your device, please send me a PM with your Roku account email address, and include the serial number of the Roku device from Settings>System>About. I'll be able to assist you further from there.