The sound was heard in several other locations, including Figueira da Foz, in the district of Coimbra. The sound was followed by a shockwave that lasted a few seconds. The causes of the mysterious sound were revealed on 28 April.

The phenomenon was reportedly felt at 12:30 pm, and social media was filled with accounts from people in the area who were confused about what had happened.

According to Euronews, firefighters did not register any incidents related to the event.

To Notícias de Coimbra, on 27 April, the Portuguese Air Force denied that it was an aircraft that may have broken the sound barrier, since at the time of the incident, the aircraft were no longer in the area. However, on 28 April, the Portuguese Air Force revealed, as quoted by Notícias ao Minuto, that it was an operational mission involving F-16M fighters, “within the scope of air defence, in which it was necessary to break the sound barrier.”