UPDATE: Metallica have announced that they will be headlining five major U.S. rock festivals in 2020, playing two sets at each. Head here for full details.

Metallica have launched a mysterious new countdown clock, which is set to expire on Thursday (Oct. 10) at 12PM ET.

The teaser timer has been posted at MetallicaXX.com, but no other details have emerged as to what this may pertain to. Naturally, the "XX" in the website URL will lead some to conclude that it has something to do with a 20th anniversary, but the group has already celebrated the only 20th anniversary within their catalog, having revisited the S&M live album, which famously merged Metallica's music with a full symphony orchestra, with two special San Francisco performances.

These S&M2 performances were captured and will hit movie theaters for a one-night only screening at 3,000 theaters worldwide on Oct. 9. So that's not it, though that seems to be the prevailing conclusion reached by fans commenting on Metallica's tweet of the countdown clock site.

At the end of September, Metallica stunned fans when they issued a statement explaining that James Hetfield had entered rehab to treat addiction. In the early 2000s, Hetfield struggled with alcohol abuse and anger issues, for which he sought treatment in the midst of the writing sessions for what would become St. Anger.

With the return to rehab came the postponement of the group's Australian and New Zealand tour dates, which were scheduled for 2019. They made no comment on the already scheduled 2020 dates and those are presumed to still be a go. For more info and tickets on future tour stops, head here.