Edit: didn't notice you said WunderRadio update, not just 2.2 in general.
If you downloaded 2.2 at the same time, it might not be WunderRadio.
Ambiance and WhiteNoise are showing similar behavior post-firmware-update; they mute at sleep, which pretty much breaks them. Also, the phone appears to hard-mute in "Silence" mode now for these apps.
Even if they fix the sleep/mute issue (which I assume is a bug) the silence switch forced-mute is unfortunate. There's a clear need to be able to turn off unexpected noises (calls, texts, etc.) and keep expected ones (the white noise generator you're sleeping to).