Oh, I see, thanks. The Google device does have a setting that seems as if it should be related, but sadly it didn't help. Based on the feedback in this thread, I'll probably have to get some new hardware.
I suppose another option is a gross hack like playing a second of silence every few minutes, since for some reason the Google Mini only bloops when it hasn't received a new connection in a little while.
YES to " Can anyone confirm that the Sonos integration will play my mp3 or wav files without any extra sounds?"
I have a Sonos home speaker ecosystem where every room as a speaker. Any speaker will play audio music files without the annoying sound that chromecast makes prior to play anything. I have a ikea symphonix picture frame that speaks text from various apps as well as play music from the File Manager.
There is a Alexa skill "My Audio" that will play your own audio files. I use the original AOL "You've got mail" announcement for my mailbox.
I've got the Ikea speakers made by Sonos.
They work great (local sounds, speaking, etc.).
I'm always pumping sounds through them so I know what's going on with my house. Upon occasion, some of the TTS things I send will get confused (probably when I send things too close together) and I'll hear an announcement from the "last" time. It's not very often and I'm pretty sure it's something in the way I'm sending stuff.
All in all, I REALLY love the way they work (I was using the integration to make my Google speakers talk) and that was a mess (too slow, way too finicky, etc.)
I keep waiting for them to pipe up with "I'm sorry, Rob, you know I can't let you do that". 
How do you like that? I've been interested in them but ended up with a bookshelf speaker to test. Turns out it works really well with the Apple echo system and complements the HomePods.
If you happen to have one of the bookshelf speakers then how do they compare?
I’ve had the picture frame speaker for several years now and really like it. The sound quality and quantity is quite a bit better than a HomePod mini. I just wish it could be made the default speaker for an Apple TV. I always have to switch to it from the HPM.
I love it. I've moved most of the speaker notifications across my apps to that picture frame. This effectively leaves the SONOS speakers throughout to home exclusively to music and the voice assistant speakers for weather alerts. I do plan to replace the office speaker with a pair of those bookshelf speakers. I've hear good things about them and they'll look better on the bookshelves.
I got a handful of the IKEA branded Sonos bookshelf speakers.
WAY cheaper than native Sonos--and they certainly let it speak and make noises for me (which is all I really wanted--just to know what it is doing at certain key times).
The cool thing is they have wall mount brackets that turn them into mini shelves--which has proven very helpful!!
Not sure if mine are Gen 1 or 2, but they are like these:
Download the Hubitat app
