I have an 04 GHS walker. Just put a new set of blades on it and now something in the deck is knocking. Gear boxes have oil. I used new shear pins on the blades. The blades themselves don't appear to be hitting anything. They don't hit each other nor the deck itself. I *think* that the problem is one of the blade shafts is somehow loose inside the gear box and allowing the blade and the shaft to travel up and down about 1/8 inch. This could possibly be enough to create the knocking sound I'm hearing (and feeling). Any idea how this could be happening? I believe the vertical shaft the blade attached to is connected to the gearbox with some kind of pin or E-clip. Could it be that this pin is worn down or broken? It's only one blade shaft that is loose. Anyone ever seen something like this before?