I've wondered about this...it slowly started after my last clutch job. Of course I replaced the throwout bearing. But my truck needed pretty much everything replaced, so along with the clutch job was all that other stuff. So this noise slowly started, but of course I just figured it was something else. The last time I did my clutch, because I had marlin work on my tranny again, I didn't change the throwout or pilot bearings. I figured "why not" on the clutch, but doing the throwout bearing meant taking it to a machine shop to press the old one off and new one on, so since I only had about 10,000 or so miles on the old ones...I just left them. I'll take photos, but the "old" clutch has some wear marks on it...I'm no mechanic, I just play one on this truck, so I have no idea what's normal, but they seemed odd. I wonder if somehow my throwout bearing isn't moving around too much or something, or was just faulty from the start.
But the wear marks were on the clutch disk, not the teeth, so that wouldn't make sense, since the noise happens with the clutch pedal out. Anyways, the fact that that's kind of the area the noise is coming from (but it's hard to tell), and the fact that it seems like some slack or something is being taken up and something's suddenly coming to a stop (loud-ish pop! when I push in the clutch sometimes..), I've been thinking it somehow had to do with the clutch, but having been in there twice in the last 3 years on this truck and seeing things put together right, I've been thinking that can't be it....
