I bought one of the new Xbox360 Slim models with a 250GB hard drive 3 months back after my old xbox had died from old age (or in other words, red ring of death).
I decided to have it standing this time instead of using a horizontal position. It was fine until recently when my cdrom-drive started causing vibrations to the xbox casing. Now this isn't a major issue considering I usually install games to the hard drive but it still is a bit annoying to listen to this loud buzzing noise for 2-3min until the cdrom decides to shut down again.
Considering it was clearly vibration related I decided to move my xbox360 to a horizontal position and the issue vanished completely. I could just leave it at that and move on but I would still like to know what is causing the sudden vibrations in vertical position and if it's possible to fix this (I actually prefer having it standing).
And yes, I always removed the cds before moving the console