This was an episode from Avengers Assemble (TV series). Although I cannot remember which season exactly, my guess is it happened after season 2 (most likely in season 3).
I think Captain America and Iron Man arrived at the entrance of a building to save people from something (an earthquake or some villains perhaps?). They might have been accompanied by 2 younger heroes, one of which was Ms. Marvel (Kamala Khan; not to be confused with Carol Danvers' former superhero identity).
At some point, the building was shaking, and then a chandelier fell from the ceiling. Iron Man looked and noticed a baby grand piano right below, so he quickly flew towards it to push it away in the nick of time. Captain America looked at him with astonishment, and the following conversation happened:
Captain America: Did you just save a piano?
Iron Man: What? It's an Austrian.
Not verbatim since I no longer remember it, but the idea was that it was a valuable piano.