I was having this issue also, what happened to me was over time my deck was becoming lower and lower, the reason was that right where the deck is welded and connects to the piece that lowers and rises the deck was getting worn, ultimately the weld broke and I needed to have it rewelded. If thats not the problem, you may need to re adjust the deck height by lowering the deck all the way to the ground to the 1st setting #1 and adjust the deck height screws. Good luck.