Depending on what you're using
Try using an amp effect.... either amp it 2x or more, or if you use a peak controller of any sort (though I'm not too familiar with those things so maybe that's not even a possible problem), make sure that's eliminated and turn the volume up a bit.
If it's just the file being uploaded that gets quiet, try converting it to a different kind of MP3 with a program such as Goldwave or something. Sometimes, MP3 files can be encoded wrong, to where even WMP wouldn't recognize them, or they would just be screwed up beyond recognition. 3/5 for potential.
Please contact me if you would like to use this in a project. We can discuss the details.