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Please be advised we are talking Avengers: Endgame, a movie where for many people literally knowing even one iota of information about the film is a ruinous spoiler!

Avengers: Endgame -- which is now playing in several international markets, including China and various European countries -- doesn’t have a mid-credits or post-credits scene per se but it does have … something you should nevertheless stick around for after the end credits are done rolling on the 181-minute superhero epic.

As with all MCU movies, the last image seen after the end credits roll in Endgame is the Marvel Studios logo. But this time, rather than a score or simply silence, there is a curious sound effect.

Spoilers ahead! Do not read further if you want to know the nature of this post-credits tag!

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As the Marvel Studios logo comes up for the final time in Avengers: Endgame, the sound of clanging metal can be heard. While there are no visual cues, the sound effect itself is most likely an aural callback to the very first MCU movie.

Our educated guess is that the clanging metal is the sound of Tony Stark forging his first Iron Man armor in the 2008 film that kicked off the entire Marvel Cinematic Universe.

But what if it’s something else? Might it instead be a nod to Eitri the giant dwarf (played by Peter Dinklage in Infinity War) who was forced to forge the Infinity Gauntlet for Thanos?

Or is it, as IGN’s Tom Jorgensen suspects, a hint that Wolverine and his adamantium claws are finally coming to the MCU?

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The safe money is on it being an Iron Man callback, but what do you think that sound effect is? Are you disappointed that Avengers: Endgame is the first MCU movie not to have a mid-credits or post-credits scene? Let us know in the comments!

And for more on Avengers: Endgame, check out our review, find out what Kevin Feige told us about the MCU's future plans, and discover our pick for the strongest Avenger!