To prevent damage occurring during transit, some front-loader washing machines are delivered with 'transit bolts' attached to the rear of the unit. These hold the drum, which usually moves freely back and forth, in a fixed location to prevent the drum from damaging the washer.
These bolts should have been removed prior to using the washer.
If you are moving house, you should reinstall the transit bolts for the move, to prevent the drum moving and the washer being damaged.
To install the bolts, access the rear of the washer, and then place one bolt in each ‘of the four holes, as shown below:

Specific information about the transit bolts in your washer can be found in the manual for your product.