If you start hearing rattling from your MMM, remove the blade pulley covers. The 4 bolts that hold the pulley together come loose, perhaps they did not torque them down correctly at the factory. I heard the rattling and smelled burnt rubber . Stopped the mower and removed the pulley cover on the left side and sure enough, only one bolt was still attached and it was loose.

It is not a tragedy, luckily. While it looks impossible, you can actually insert new bolts up from the bottom of the pulley without removing the pulley. Repair process:

1. Lower MMM to bottom with height set to zero.
2. Remove plastic pulley cover. (two knobs)
3. Unhook tension spring on port (left) side of mower deck. I used a 2 foot crow bar and a 3 foot piece of 2x4 set against the wheel and the drive pulley for levearge.
4. The belt comes off easily.
5. Align the pulley holders 4 holes with the holes in the pulley.
6. Take a new M8 (1.25 thread) bolt (same length as the original) and carefully try to insert it in one of the four holes underneath the pulley. I have big hands and fingers and I could do it, though it seems hopeless at first. Put a lock washer on the bolt and loosely screw an M8 nut on the end.
7. Do this for all four holes.
8. Block the blade with a piece of wood.
9. Carefully use an open end wrench to hold the head of the bolt from underneath the pulley. It is difficult but an open end wrench works. A crow's foot might be easier but i don't have crow's foot wrenches.
10. Tighten the nuts as tight as you can with a ratchet wrench.