I was repairing a rider last week for a customer who complained that when he went to engage the blades the mower had a clicking sound and the blades would not turn. I flipped it on its side and removed about 50 pounds of 3 and 4 inch thick mud from under the deck. Once the deck was cleared the blades had room to turn and the problem was solved. Another good reason not to mow when the ground is wet.