Megadeth's 1990 album Rust in Peace is one of the best thrash albums ever made, but it was recorded in absolutely chaotic circumstances.
Dave Mustaine had fired most of his band in 1988: guitarist Jeff Young and drummer Chuck Behler were out. After auditioning many musicians, former Cacophony guitarist Marty Friedman joined the band while Behler's tech Nick Menza took over on drums.