If a washing machine is noisy while spinning the usual cause is worn or damaged drum bearings. This normally causes a rumble sound that gets progressively worse as each time the machine is used. The noise could also be worn motor bearings or if more of a knock than a rumble, check that the weights have not worked loose and the dampers that support the tub are ok.
To establish if the noise is being caused by either drum bearings or motor bearing, remove the belt and rotate the drum by hand. It should turn smoothly and quietly. Re- fit the belt and try again, if it now sounds louder it is probably motor bearings at fault. This usually entails the fitting of a new motor.
Failing drum bearings are often accompanied by a leak of rust coloured water down the backplate of the tub and even, in some cases, onto the items being washed.
Drum bearings generally consist of two bearings, one larger than the other, and a seal. The seal often fails first causing the grease inside the bearings to be washed out and the damage spreads from there. It is very important to catch bearing failures early to prevent further damage to expensive items such as the drum shaft or the housing that the bearings fit into. Also, the leaking rusty water mentioned above, may find its way onto electrical parts below such as the motor and heater terminals.
Many machines now have one or two piece plastic tubs into which the bearings are fitted, this involves a major strip down and often the use of special tools to extract and fit the bearings themselves. Some older machines, and a few newer ones, use metal tubs with a cast bearing housing bolted on at the rear which can be removed for easier fitting of bearings.
In all cases, check the condition of the shaft which fits through the bearings as well as the housing itself as damage to these can often render a machine beyond economical repair.