Distorted/Scratchy audio from CDROM2 system

[TEKWRX]

I recently got a CD-ROM2 set-up with the interface unit.  It seemed to work fine, but now I notice that the CD audio is somewhat scratchy.  Not all the time, just on the high parts of the music.  It's hard to describe.  I happens with games or with audio CD's.  When I plug headphones directly to the CD-ROM, it sounds clean and perfect, so it must be a problem with the IFU-30 interface unit.  I have the special bit to take out the screws, but I would have no idea what to check for.  Anybody have any ideas?