There's no completion date for the follow-up to 2008's Death Magnetic, although drummer Lars Ulrich recently said they were aiming to include some of the material in this year's summer shows.

Trujillo tells Rolling Stone: "We're working on these songs, we are being productive and having fun." Asked whether the music feels like an extension of Death Magnetic, he replies: "I can't say that yet. I can't relate it to any album - I think every Metallica album is unique."