I used to use Calm for that, but they blocked it off for only their paying customers. I think I ended up finding another one by doing a search on iHeart radio, or something along those lines. I was using the search term “thunderstorm”, but I’d imagine you could come up with something like “nature” or some other search term, once you’ve installed the various “plug-ins” for Sonos. Shoot, I’d be tempted to search outside of Sonos, and then just install the one service that I found that provided it. 

“Zen Nature Serenity” on Amazon Music has some good forest sounds.

Sonos Radio has a free Rain Forest station if that works. I use the Calm App as I got it for free as an educator. It is a great app and has a tremendous amount of options. Also if you have Apple Music or Amazon they have a ton of options as well. 

Thanks to everyone. It’s been quite helpful.