This problem is not present on Roku 2 devices with firmware version 4.1 build version 2669 (I might have the build number incorrect but the version is certainly 4.1). The problem was introduced in the version 4.2 build 1007. I am positive on this since we compared two Roku 2 boxes in our lab - one was at version 4.1 the other at 4.2. The first one did not exhibit the behavior (below) the 4.2 one did. Later, after upgrading the first box to 4.2 it displayed the same symptoms.
1. Turn on Roku 2 on an HLS stream and let it run
2. After some time of running it the playback starts to run at an accelerated mode (like rewinding an old-fashioned VHS tape) with a loud screeching noise
NOTE: the problem occurs very rarely (prob. once every 100 hours of recording). It happens at exactly the same spot on a given stream every time. It doesn't matter when the playback was started, it certainly looks like there's something in the stream it doesn't like. I don't believe there's anything wrong with the stream though. If the user rewinds the "accelerated-screechy" stream back to the point where the artifacts appear the playback restarts normally, no artifacts present. This makes me think there's something wrong with the way the stream is processed. Once more, the problem is not present with the Roku 2 firmware version 4.1 or earlier.
I saved off a sample of a stream which exhibits this behavior and can present it to the troubleshooting team upon request.