[codyace]

I'd put money on input shaft bearing, or similar internally. It's strangly more common than the forums lead you to believe, and your symptoms are almost dead-nuts on in regard to how it works. Intermittent, and random, and only when clutch depressed.

Some people like to write it off as a TOB issue, but even on cars with NEW TOB's you can get this noise.

In regard to the clutch touching through overextension, you can't do that unless you have the totally wrong (thicker) TOB in it, or a silly long rod in the slave cylinder for some unknown reason.