→ It might be cause either by an unbalanced load of laundry, or some foreign substance.
The washing tub rotates at a quick speed during a spin cycle. If a load of laundry is small
(i.e. one or two pairs of jeans) or big(i.e. several blankets), the tub may become unbalanced
to one side, giving rise to a bumping sound. Ensure that laundry is evenly distributed or add
or take out some of the laundry to fit the recommended amount of laundry.
Especially, when you wash a blanket, make sure to only roll up one blanket at a time.