CD changer problem

[donseclipse]

I have 2 problems.
1. I have a 10-disc sony cd changer in the trunk now it works only occasionally and when it does work.. it makes a hissing sound every other second or so... now this is nothing wrong with the speakers since the radio works fine. It just goes through all the discs and skips them all although there are cds in them and gives a 'E-04' sign on the deck display.
2. my in dash head unit also has a cd slot so when i put a cd into it.. not always but most of the time is makes a lot of noise like its scratching the cd and then it kicks the cd out.
Im sure some of you have encountered or heard of such situations before.
Help pls