i have an 07- silverado 1500 classic/with 4.3- 5 speed standard.
after truck sits in the garage for a few days, only sometimes,not always , when i engage the clutch an put trans in gear an let clutch out the clutch will chatter , anly in reverse an 1st gear. now after a couple or three uses the chatter goes away an clutch is normal. there is no sign of any water or oil leakage so that is not the prob. also there is no problem putting it gear, just as i'm letting the clutch pedal out.

 

You may have oil on the clutch plate or the release bearing binding on transmission bearing retainer.

 

that was my first concern because the chatter felt like the clutch was wet. so i went underneath an i turned the flywheel over by hand an snooped up through a little inspection hole to check for oil , as in rear main leaking an i didnt see any, it was dry, now as for the throwout bearing sticking i cant see that, but that could be a problem cause of a hydraulic linkage. so what do you think if i was to push pedal down an release it a couple times before i put it in gear. Thanks for your reply!!!