I've been thinking about this myself.
The only idea i've come up with, but yet to be tested, is to load some sounds onto old phone, then connect this to bluetooth speaker hidden somewhere behind or under the layout. You could then use a music app on the phone to select the appropriate sounds as and when. required. Personally i was thinking of a background country sound/weather sound and have this play on repeat. I can't remember where now but i did find online a site where these sorts of sounds could be downloaded for free, something tells me it was the BBC sound effect department.