TECH HELP!

I absolutely CANNOT get a file to convert from mp4 (recorded on my iPhone, plays beautifully in all media) to mp3 (which I need for a job.)

I get distorted sound out of the end product. I've tried converting it to .ogg and then to mp3, but it fails every time. HELP!! Anyone? Thanks to mosreal I was able to get my iTunes program re-set to do it for me, with success. THANK YOU for so quickly offering me your help, I really appreciate it!