Sound works in iOS simulator but not on device?

I’ve ported 6 WP7 XNA games to iOS (and Android) via MonoGame. For some reason, the sound is not working on my iOS device (an iPhone 5S running iOS 7.1)

The sound is fine in the iOS simulator (the one that comes with Xcode) - I’ve tried a variety of simulator devices and they’re all fine. But when I deploy the same code to my iPhone from Xamarin Studio, the game runs fine - i.e. no errors/exceptions - but there is no sound.

I’ve checked all the obvious things (the phone’s not on silent, not unexpectedly paired with a Bluetooth device, and I can’t find any obscure sound settings on the device). Other apps play sound fine.

In order to get SFX working at all, I had to follow the suggestion in this thread: Phone music while app running - I don’t understand how that can be working at all, so I’m rather suspicious of it.

This is affecting both SFX (.wav) and Music (.mp3)

Any ideas?

Ignore me, move along, nothing to see here…

(slaps forehead)