I'm pretty sure the problem was in that little device that I use to boast the volume. I changed the two AA batteries in this little unit and I still got distortion. When I disconnected the device and played the mp3's there was no distortion.
So, I check it on a gig this week end and I'll know for sure.

Also, Eddie, btweengigs, suggested using a program call MP3Gain which is free. This program takes all your mp3's and evens out the volumes so that when you go from one mp3 to another the volumes don't change drastically.

I'll check it out this week-end.