Based on our investigation, we believe this may be an issue specifically with the firmware on the Roku 2 or lower. (Please let us know if you’ve seen it on the 3 as we weren’t able to reproduce it on that model.)
When transitioning to or from commercials feeds, broadcasters introduce a period of silence. What appears to be happening is that the Roku is employing a form of dynamic range compression, ie. they are boosting volume for very quiet segments and damping volume on very loud segments.
When encountering silence, the Roku may be over amplifying the audio causing clipping when full volume is suddenly resumed, which would account for a loud chirp sound. Following, we immediately hear a sudden drop and fade-in back to a normal volume level, again consistent with dynamic range compression.
For example, the graph below shows the wave form of the audio when transitioning out of a commercial. We hear the chirp when the volume is abruptly restored. The second graph is just an illustration to show that we do indeed have complete silence. Applying a huge amplification does not affect the silent period.
Regular wave form:
Amplified wave form:
Long story short, we’ll be working with the Roku team to adjust their settings for this or give us an option to disable it.