Hi this sounds like a failed bearing in the motor.
The motor bearing is damaged when the vacuum filters are not regularly cleaned, which results in the motor overheating, unfortunately changing a motor's bearings is very difficult and in most cases results in the entire motor being replaced.
The vacuum should still work all though it will be noisy, the noise will also get louder as the fault gets worse, and eventually the motor will stop all together.
A quick look online shows a new one costs around £60, such as the one here. A new motor will cost upwards of £50, my suggestion is to contact the Zanussi service centre on 03445 614 614, to see if you can get a reconditioned unit in exchange for your existing one, as I believe this would be an uneconomical repair.