Rob has a Roku app that's making odd noises in his Home Theater system. It's part of his TCL 6-series that's hooked into his Denon receiver via HDMI through the audio return channel (ARC). Leo isn't much of a fan of the apps built into smart TVs. They are almost never updated and usually are poorly written. Leo says it sounds like an encoding issue with Dolby. Look in the TV settings (or the Roku Stick settings) and either turn it on (if it's off) or off (if it's on). Set it for PCM and it should fix it. See if that fixes the problem.
Scott Wilkinson says it's likely a decoding issue, and he thinks that the receiver isn't understanding the encoding a five-year-old receiver isn't getting.