A little bit of background..
I have speakers in different rooms, and have set them up to reflect this. We have an echo dot in the living room, which is connected via the Sonos skill.
I often listen to music in my study while the kids are in the living room.
I began to notice the volume on my speakers started to occasionally dim for no seemingly reason, then would go back to normal a few seconds later. Typically it was worse when the kids were home.
After a lot of troubleshooting, I figured out that Alexa isn't Sonos room aware. This means whenever she is activated (be it on purpose or by accident), she will dim the music on ALL speakers in the house to allow you to hear her.
I have logged a call with Sonos support, who have requested I post on the community forum to explain the problem I've found, while they pass it onto their development team.
The other down-side to having multiple rooms setup is that you have to stipulate 'Alexa - play SONG on SPEAKER'. She also isn't aware of my music library and will only play songs from Amazon. Has anyone else found a way around this?