iPod mini sound output is too quiet

Hello all,

I've had a second-gen iPod mini for about a year now (bought it refurbished from Apple) but recently it stopped played music, or so it would seem. At first it stopped playing the frequency on which voices are heard (which in effect, turned it into a karaoke machine) but after that it stopped playing music. All of its other functions work just fine. However, one day, I plugged it into a speaker, turned the volume all the way up, and when I held the speaker to my ear I heard the music very faintly. So apparently, it's playing the music, just ridiculously quietly. Does anyone have any idea why this happened and what I can do about it?

Thanks!