A Washington state trooper who pulled over a semitrailer for speeding discovered a mobile music studio in the cab, complete with a computer and a microphone that dropped down from the ceiling. Oh, and suspected drugs.

Trooper Chris Thorson, a spokesman for the Washington State Patrol, said the driver acknowledged producing music while he drives, an activity that Thorson called “incredibly dangerous.”

“I’ve been doing this over 20 years. I’ve never heard of such a thing,” said Thorson, who shared the story on Twitter this week.

The 31-year-old driver was stopped at the town of Kennewick in southeastern Washington on Dec. 31 after a trooper saw him driving aggressively and 17 mph over the speed limit, Thorson said. He was arrested — not for making music, but on a DUI charge after the trooper smelled marijuana in the cab. Police also found white crystals that they suspected were drugs.

Thorson said the trooper making the stop noticed that a computer screen was on, showing what looked to be music production software. Thorson posted a picture of the setup Monday after recently learning about the arrest.

“The driver admitted, ‘Yeah, I produce music while I’m driving down the road,’ ” Thorson said. “He does it all behind the steering wheel.”

The trucker, who lives in Florida, could not be reached for comment, but a Facebook page in his name includes several streaming videos shot from inside a truck cab at night with rap music playing. It’s not clear whether the driver is in fact the one heard rapping in the videos.