Anon is partly right. It could be bearings or it could be something caught between the inner and outer drums.
If the drum makes a noise when you turn it by hand, or it moves up and down on it's shaft then it will be the bearings.
Now, if the machine has been making a noise for some time and the movement is excessive, then it's time for a new machine . This is because the plastic outer drum housing will not hold a new bearing race securely, and the price of a new housing with labour is almost the price of a new machine. Only when it's dismantled will you see the full damage.
Maximo, July 2008