The statements came in testimony Tuesday in the trial of a federal lawsuit brought by a producer who worked on the first two White Stripes albums and asserts that he deserves a share of the royalties. The trial began Monday.
The suit was brought by Jim Diamond, who is listed as co-producer on the band's self-titled first album, released in 1999. He is listed as sound mixer on "De Stijl," released in 2000.
In an aside to Diamond's claim about the note, White and Jason Stollsteimer of the Von Bondies testified about their fight inside a Detroit nightclub in 2003. Stollsteimer also told of finding a message he said was from White.
"I found a note stuck to my door with a knife in it," Stollsteimer told a U.S. District Court jury.
The knife held up a magazine interview story in which White apparently believed that Stollsteimer slighted him by minimizing his role in producing a Von Bondies album.
The article, Stollsteimer said, had written across it: "That's the last ... time I help you out."
Earlier, White said it was "a laughable lie" that he stuck a knife in Stollsteimer's door.
White pleaded guilty in 2004 to misdemeanor assault and battery in connection with the fight.
The trial before U.S. District Judge Avern Cohn was expected to last about a week.
The White Stripes deny that Diamond helped create the band's style. The band said in court documents that it paid him $35 an hour for time at his Ghetto Recorders studio, which he started in 1996.
White Stripes drummer Meg White testified that although the group's first album listed Diamond as co-producer, he really was not. She said credit for producing that album belonged solely to Jack White.