1) Whenever I start my computer, the CPU fan makes a lot of noise and the noise remains until the desktop appears completely. I thought that the problem was with the fan, so I replaced it recently with a new one. But the noise problem is still there, which means that the problem is with something else.
2) DVD R/W tray frequently fails to open whenever the eject button is pressed. I either have to hit the case a few times so hard that it might break someone's head or pull the tray by sticking my fingers on both of its sides.
Your system runs the fan at full speed till the boot up is complete and CoolnQuiet kicks in (enhanced speed step if you run intel). Get an RPM regulator from Zalman (for instance) like Fanmate-2 or smth.
2) A jam somewhere inside. Scrap the drive, since a new one will set you back like 30 bucks or so.