My 2XS has been giving good service for years, but for some couple of months has been delivering garbled/artifacted audio on some but not all streams. I can provide the following information:
The artifacts in question sound like old-school MP3 ringing or phasing/multi-echo compression artifacts. Very noticeable in engine noises (street scenes) and on "s" sounds or heel clicks. It's very distracting in these scenes! Problem occurs in multiple channels including Netflix, Amazon, and others.
BUT, in the Amazon channel it's possible to choose from "AACH_32K", "AACH_64K" and "AACL_128K" stereo audio tracks, at least in the new series "Endeavour" (presumably among others). The issue is only present in the AACH tracks and not in the AACL track, which sounds A-OK. (I have stereo setup only, no surround.) The different names suggest perhaps the streamer isn't decoding the (quite common) HE-AAC correctly but is good with AAC-LC? I'm kind of guessing here, though. Haven't wanted to hassle with dropping a bunch of test files onto a USB stick yet as that sounds like a Royal Pain and wouldn't solve the problem.
Factory reset has been of no use. Issue occurs both on HDMI output to TV (Samsung 24" LCD 1920x1200 T240HD, supporting HDCP 1.4 according to the Roku, in both 1080p and 720p) and headphone jack on Roku. Firmware is up to date 8.0 as of 2018-2-25 but issue occurred with earlier versions (7.something at least, possibly earlier). Internet is wired Ethernet to cable connection and has been fine before. Issue occurs reliably on problem streams and not on non-problem streams.