'AGT' Metal Grandpa: Drowning Pool Wants 82-Year-Old to Join Band!

82-year-old John Hetlinger just got an offer he can't refuse ... to go onstage with the wildly popular metal group Drowning Pool for an encore performance of "Bodies."

John rocked the audience of "America's Got Talent" with his rendition, and now Pool guitarist C.J. Pierce is trying to track down the grandpa.

The goal is to get John to Chicago for the Open Air Festival in July. C.J. says they'll cover John's travel and beer expenses ... and whatever else it takes.