Excessive vibration is usually due to an unbalanced load. But you should also check these issues:
Levelling – Make sure the machine is properly levelled side-to-side and front-to-back.
Mounting – Ensure that the machine is securely fixed to the floor on all mounting feet.
Load distribution – Redistribute laundry if unbalanced. Only wash very heavy items with light items.
Worn suspension – Shocks and struts may need replacing if worn out.
Drive pulley – The pulley should turn smoothly and be securely fastened to the shaft.