mild clunking noise at idle from tranny area

Hey guys
wondering what you guys thought. I have been hearing a not heavy but many mild clunking noise coming from the tranny area at idle. And yesterday while fueling up with truck idling, it was happening on a more regular basis. In the past maybe 1 or 2 times every minute but yesterday it was several times a minute at the last couple minutes of fueling up. I don't seem to notice it when I am driving. I have not tried to see if it dissappears when I depress the clutch but since I am going to do a PM on it today, I am going to try it. Could this be a Pilot or Throwout bearing? I was under the impression that a bad Pilot will make more towards a whine than a clunk. Let me know you thoughts. Also did not know if an output shaft bearing could also be a culprit but was doubting that.

 

Yep had my nephew come over and push the clutch in while idling while I was underneath and it made a hell of a noise when he depressed it so sounds like that is it.