I thought it was my PSP... but no.
I found a freebie converter that turns YouTube videos into mpeg4 files for my PSP. Works great and the volume of sound is great too.
When I use DVD Fab for a DVD movie burn to mpeg4 the sound quality (even at 150%) is very poor and I have to turn up the PSP volume max... or use headphones
If anybody could tell me how to great a better sound transfer, I would be most grateful.