Unlike most Marvel movies, Avengers: Endgame did not have a post-credits. Instead, there was a very familiar sound at the end of it.

Warning: This post contains MAJOR spoilers for Avengers: Endgame.

As we all know Endgame marks the end of the MCU era, which all started with 2008's Iron Man. But though this chapter has officially come to an end, fans waited for some sort of clue about what's going to happen next. Unfortunately, there weren't any. But there was something. A clanking noise begins to play over the credits... the sound of a hammer on metal.

According to Entertainment Weekly, it's a subtle tribute to the first Iron Man movie in which viewers saw Tony Stark making his first suit while he's trapped in a cave in Afghanistan. He sacrifices himself at the end of Endgame to save the rest of humanity, so the noise could be a nod to the movie and the character that started it all.

However, other people have theorized the sound could be a teaser for what's coming next. After all, Tony Stark isn't the only Iron Man in the comics—and though we're going to miss Robert Downey Jr., perhaps another Iron Man will take his place in future films. The clanking could be the sound of another person making his or her own suit.

We'll just have to wait for the next film to know for sure.