More than likely the dvd tray tracks are misaligned. The way I would fix this problem would be to take the unit apart and carefully examine the tray gears.
Most of them are essentially the same and you won't need a manual or anything to figure it out, just patience and common sense.
Sony does have service manuals for just about every product they've ever made, but access to them is limited to Sony employees / techs.
There are a few places online that sell copies of these manuals but like I said earlier, patience and common sense are going to be the quintessential tools for fixing this problem.
- Unplug the dvd unit.
- Take it apart, check the gears.
- Plug it back in to see where the clicking is coming from exactly. -- Be careful not to touch anything, you don't want to damage anything or worse shock yourself.
- Unplug the unit.
- Get the gears back on track.
- Plug it back in and see if it's fixed.
- Once everything's working again put it all back together.
It's not under warranty still right?
Get back to me if you get stuck or have more questions. You can also upload pictures and videos if you want to give me a closer look at the problem.