The actors are all competent musicians, and they're actually playing on the soundtrack.
Harry Shearer, Rob Reiner, Christopher Guest and Michael McKean were given $10,000 to write a script. They made a 20-minute version of the film to better demonstrate the improvisation they had in mind. Several scenes from the demo are in the finished movie.
After the film opened, several people told Rob Reiner that they loved the film but he should have chosen a more well-known band for a documentary.
Several rock stars have commented on what an uncannily accurate spoof of the rock and heavy metal world this film was. Ozzy Osbourne said when he first watched the film, he was the only person who wasn't laughing; he thought it was a real documentary. U2 guitarist The Edge said, "I didn't laugh, I wept. It was so close to the truth." Marillion had five drummers in the space of a year between their first two albums, which guitarist Steve Rothery later admitted was "like Spinal Tap".
During the metal detector scene, the background voices making announcements over the PA are the band members without their English accents.