Rattley idle

Also known as:
Noisy gearbox
Noisy flywheel

What is it?
Itís either the manual gearbox or the flywheel. A light rattling noise is usually the gearbox due to itís construction, and as the gearbox warms up and tolerances close the rattling dies down. A louder rattle could be the flywheel getting tired.

Usually caused by:
Old flywheel
Cold manual gearbox

The manual box has some very tight tolerances to deal with the power it can handle, but the tradeoff is a positive shift action, a rattle when cold, and no tolerance to sloppy gearshifts As the Ďbox warms up the tolerances close up and the rattle goes away.
The stock flywheel is a dual mass sprung unit. This means itís got a mechanism for damping drivetrain shunts instead of having a sprung clutch plate. When itís getting old things get loose in the sprung/dampened areas and a rattle occurs.

How bad is this problem?
The manual box noise is normal.
The flywheel, when rattley, still has life left in it, but itís best replaced when the clutch is next swapped out.