What is the causes of vibration in automobile engine?

Mechanical looseness, misalignment of internal bearings, misalignment to or from a driven load, bent or distorted rotating components, failed bearings, worn bearing housings, worn bearing journals, misalignment of rabbet fits, improper mounting, soft foot, structural defects in mounting hardware or surfaces, dynamic balance of all rotating components, conflicts with natural frequencies in the area of or connected to the device.