Sound from Music App garbled excess reverb echo like iPhone 4S

I am experiencing a sound distortion when listening to my Music app. It sounds like a reverberation on a small band of frequencies, towards the lowere end, almost echo like, giving a garbled background noise to the sound. This is hardley percievable with music, but heard very clearly in voice programs such as my podcasts. This reverb/echo is not present with sound from other apps - phone calls do not experience this, YouTube videos do not have this in the audio, nor does streaming audio from other apps such as the Public Radio app. This is only present in the Musc app.

I've restarted the phone but the sound persists. I've also gone in to iTunes and adjusted the sound level under the Options tab of the info window, and reloaded all of the podcast files. No change. This is heard through the headphones, through my car's audo system, and also through the built in speaker of the phone. I don't use any bluetooth audio devices so I've not tested that.

Any explanation?

iPhone 4s with iOS 5.01