Unloaded at a yard today and fired up the mower only to hear a horrible knocking and grinding sound...so I quickly killed it. Turns out that last night I tried to tighten the blades on in reverse with my impact!! The blade bolts were so loose that I used my 2 fingers to unscrew them!! I am not sure what would have happened if they would have come off, but it wouldn't have been good! My lesson learned is to never sharpen blades at 11:30pm when you half asleep.