Today after pulling out of my driveway, I noticed a slight vibration in the clutch pedal area (similar feeling and sound to that of having a big nail or rock stuck in your tire, not as bad as an unbalanced wheel).

The engine was partially warmed up. After a stop for coffee, this seems to have gone away. Not going to freak out about it, but will pay attention to see if it continues happening.

Any thoughts as to what it may be?