Well I'm kind of an audio nerd, and the radios are great to listen to in the background, so I guess that explains it.
You probably can't find it, but it's relatively easy to figure out by just browsing the original game files, since the audio files (except for SFX.RAW/DAT) are all unpacked.
The most damning piece of evidence is that they have twice the encoder delay (mp3 encoders add a few samples at the beginning and end) that the file would have if encoded once (from VC PS2 for example).
You probably can't find it, but it's relatively easy to figure out by just browsing the original game files, since the audio files (except for SFX.RAW/DAT) are all unpacked.