In the hustle and bustle of a large city like Zurich, it’s hard for a single noise to rise above the humdrum of streets and give residents pause. However, that is exactly what happened over the last week, with residents of the Swiss city reporting a series of loud bangs. While theories continue to swirl regarding what caused the weird noise, experts are still largely at a loss.

Loud banging noise heard across Zurich

According to residents, the mysterious banging noise was heard in Zurich over the last week, peaking on the evening of February 21 and the morning of February 22. Kreis 9 (Altstetten and Albisrieden) was the most affected, although several loud bangs were also been reported in Kreis 3 (Wiedikon) and Kreis 5 (Industriequartier).

Residents speaking to the Tages-Anzeiger reported that the bangs range in volume, from quiet as a church mouse to full-on cacophony. People described the sound as similar to a heavily loaded pallet falling to Earth from a great height, an explosion or a sonic boom caused by aircraft.

Zurich officials are at a loss to explain the loud bangs

Naturally, locals and the media soon donned their deerstalkers and attempted to find the source of the odd noise. Their first port of call was construction sites, as they have more than enough potential to cause a loud noise by accident. The theory also matches the location, with Kreis 9 being notable for many new construction sites for housing and offices.

However, this theory was quickly thrown out, with a spokesperson for the Zurich civil engineering department stating that construction sites “cannot be the cause.” “The district chief of the Zurich city police has also received such enquiries in the past and cannot explain the noises either,” they explained, adding that maybe Cargo Sous Terrain or the Federal Roads Office (Astra) were responsible for the noise.

Cargo Sous Terrain - the new billion-franc underground freight line set to run from Zurich - told the Tages-Anzeiger that it couldn’t be them as they had stopped drilling in the city in August 2023. Astra said that while there was some work going on at a nearby motorway, it could not be responsible for the bangs.

Could construction walls be the source?

With all the likely suspects equipped with air-tight alibis, officials at the Koch Areal - a massive construction site in Zurich - created a unique theory of their own. They told the Tages-Anzeiger that plates used in sheet piling - a type of wall used on construction sites to secure holes and pits - change in size depending on the weather, expanding during warm conditions and contracting with the cold, similar to how a baking tray can warp itself when exposed to oven temperatures.

During these expansions and contractions, parts of the structures could produce a banging sound. With the weather recently going from hot to cold back to hot in quick succession, this could explain the loud banging noises once and for all.

What do you think is causing the loud bangs in Zurich?

However, the Tages-Anzeiger noted that while the theory is plausible, it would be impossible to blame a specific construction site for the banging, meaning that, for now at least, the case remains open. Do you have a theory about what is causing the banging? Let us know in the comments below!