LUBA 2/2X cutting deck making a loud, diesel-engine-like or grinding noise

The symptom

Owners describe it as sounding like a diesel engine, sometimes extremely loud. It comes from the cutting deck itself, and the dealer's diagnosis: most cases trace back to grass compacting on top of the blade discs until it's thick enough that the blades physically flex under the pressure and strike each other¹.

Cause 1: grass buildup flexing the blades into each other (most common)

The same underlying mechanism as the cutting-height failure covered elsewhere on this site — grass compacts on top of the blade discs — but here it causes the blade discs to flex enough that blades on adjacent discs physically touch and chatter against each other¹. See our cutting-height system failure guide for the full mechanism and prevention tips (mow more often at lower height, expect a "fighting the lawn" period on new installs).

Cause 2: worn blade screws letting a disc shift

A more specific, compounding cause: the screws holding each blade to its disc wear down at the back over repeated rotation, letting the blade shift outward by a millimeter or two. Combined with grass buildup pushing discs up slightly, this is enough for blades to start touching that otherwise wouldn't¹.

The dealer's standing rule: never reuse blade screws. Replace them every time you replace blades, even if a screw looks undamaged — this is stated as the single most important habit for preventing this specific noise¹.

Cause 3: a loose disc-retaining nut

A reported case: a horrible squealing noise, present specifically at startup and shutdown but not during normal running, turned out to be a loose 10mm nut in the center of a blade disc. The loose disc had worn a groove into its collar, and the collar itself was then rubbing against the motor housing¹. If your noise pattern matches (squeal at start/stop, quiet in between), check disc nut tightness before assuming a bearing.

Cause 4: sticks or debris trapped where you can't see them

Small sticks and fibrous grass/seeds can lodge under the blade discs and collar in spots that aren't visible without disassembly — the dealer notes owners routinely insist "there's nothing under there" until the deck is actually pulled apart¹. The fix requires removing the discs, blade guards, and the collar itself to check underneath — a routine part of proper cleaning, not a special procedure. See our cutting-height guide for a step-by-step disassembly procedure covering this same area.

Cause 5: a worn bearing (uncommon on LUBA 2/2X)

If none of the above applies, the remaining possibility is a worn drive-motor bearing — described as a distinct "grinding" or occasionally squeaky sound, not the sharper chatter of blades touching. The dealer notes this was common on the original LUBA 1 but has been rare on LUBA 2¹, and links it to prolonged exposure to wet grass or standing water. Self-test: remove the blade discs entirely and run the mower in manual mode. If the noise persists with no discs installed, it's coming from the motor itself, not the blades or debris¹.