You should probably call Sonos about this. This seems to hit your system only.

Other people are impacted by it. Such as myself.

Subsequent to firmware upgrade 2 days ago, some speakers began 'lisping' the high ranges (the sound approximately like having the gain set too high). 

Mixed-generations system; only the Play:1 (ca. 2012) units are effected. My Move2s and my Era100 playback are normal. This occurs across multiple streaming services (Soundtracks by Spotify being the most prominent effect).

On the year of breaking updates, a barely useable app (it still shows "No Content" most of the time that I open the mobile app while music is playing; if I'm lucky I'll see a song title that played 5 minutes ago after leaving the app open for about 8 minutes), you guys actually now degrading the audio quality on hardware that I have spent years blasting about and telling people they should buy, is feeling like a lot of sand in the face.