When you record too loud, your mic cannot hold the wave amplitude and it clips it... that is, it chops off the top (and bottom) of the waveform so that it fits in the maximum amplitude it can handle.
That's what clipping is, and it introduces degradation of sound quality.
That said... Why did you record your VB in mp3? And you packaged wav+mp3 too, that makes the file unnecessarily large. I'd suggest you to drop that trial mp3 recorder you're using and use something that can record directly in wav, like oremo or audacity...
Anyway, I opened only a few of your samples in Audacity. Some of them were good, but some have clipping (for instance, "da" and "ba" have definitely clipping)... I don't have time to look through them all, though... you should use some audio editor like audacity and look through the waveforms, if you see the top or the bottom of the wave is squared, then it meas it's clipping.