Metallica has not done a full-length U.S. tour in more than seven years, but if this new rumor is true, the heavy metal icons will be back this Summer. According to Blabbermouth, Metallica will be teaming up with Avenged Sevenfold and Volbeat for a U.S. stadium tour in twenty cities this Summer. While no official announcement has been made, this seems pretty legit, and we are expecting it to be confirmed later this month. Stay tuned…