My grandmother has an MTD (13AT604G401) riding mower. The other day, she described a grinding noise coming from under the mower and she said it felt like it has less power. I checked the blades, I checked both spindles, I checked the belt. I have mechanical ability and everything seemed as it should (nothing in the blade area was loose, bent, binding etc.) and I was unable to recreate symptoms she described. The one thing that seemed strange to me (having never worked on a PTO clutch) was that when I grabbed hold of the clutch, I could move the entire unit in a back and forth motion (think washing machine agitator) about a half turn followed by a thunk noise on metal, then twist half turn back and another thunk. Is this normal for a PTO clutch? I was going to adjust the air gap using the adjuster bolts, but I can tell this will not impact the clunking of the PTO itself. I am thinking something is wrong in relation to the engine shaft itself (bearing? idler?)