Thanks for all the input guys. Its making that sound like a bb is jammed in the barrel, not a grinding sound. The piston is in excellent shape. I think it may be the hopup rubber. Thanks coachster. I remember it being a little torn. Just to clarify, it makes this 'jammed' sound for the first couple dry fire shots, then is fine after that. Then if I let is sit for say 15 min, i pick it up, dry fire it, and it makes that sound for the first couple shots. Very weird problem :/.