I sympathize with you man. I had the same problem when I recorded stuff from my XP50 to my VS840. I also had the same problem when I ran my XP50 through an amp.

The problem seems to be the XP50's circutry. I say that because when i got my XP60 yesterday, my problem was solved. What you can do is spend $80 on a Hum Canceler/Signal Magnifier. These boxes reduce hum and noise and amplify low signals to the max which is helpful because the background noise creeps up when the XP50's volume is raised too high.