Visually inspect the mounts for looseness and cracks. To get a better look at the condition of the mounts, pull up and push down on the transaxle case while watching the mount. If the mount's rubber separates from the metal plate or the case moves up but not down, replace the mount. If there is movement between the metal plates and its attaching point on the frame, tighten the attaching bolts to an appropriate torque.
Then, from the driver's seat, apply the foot brake, set the parking brake, and start the engine.