The rumbling was so loud it sent workers rushing to their office windows to scan city streets. But the ruckus had long passed before they realized it had emanated from above.

Two F-16 jets with the Minnesota Air National Guard’s 148th Fighter Wing in Duluth practiced a flyover over downtown Minneapolis just before 3 p.m. Wednesday. The planned U.S. Air Force training exercise sent reverberations so loud that it set off some car alarms, witnesses said.

“Don’t ask for the video,” Philadelphia news reporter Sarah Bloomquist tweeted. “They came and went before anyone could pull out a cellphone.”

The aircraft are part of the military’s air defense mission during Super Bowl LII, held this Sunday at U.S. Bank Stadium. A media demonstration simulated F-16s intercepting a Cessna from the Civil Air Patrol’s Minnesota Wing flying into restricted Super Bowl airspace.

“Today was just about showcasing a firsthand look at that air defense mission,” said Maj. Andrew Scott, spokesman for 601st Air Operations Center. He declined to say how many fighter jets would enforce air defense in Minneapolis.

On game day, the Federal Aviation Administration (FAA) will implement a temporary flight restriction zone spanning 30 nautical miles around the stadium that prohibits drones and other noncommerical air traffic — as it has around major events since the 9/11 terrorist attacks.

For the first time ever, U.S. Air Force Heritage Flight will perform the scheduled Super Bowl flyover. The fleet, consisting of one F-16 Fighting Falcon, two A-10 Thunderbolt IIs, and one P-51 Mustang, will fly in diamond formation over the arena ahead of the 5:30 p.m. kickoff.