US gamers can import tracks from Guitar Hero Metallica into Warriors or Rock for free – for one week only.
39 of Metallica's on-disc tracks will be available to import directly to the Guitar Hero music library from 28th September, the date of Warriors or Rock's US release.
Buy Warriors of Rock between its launch date and 5th October and you'll be able to import the tracks for free.
Otherwise, it'll cost 480 Microsoft Points (£4.11 / €5.76) on Xbox 360, $5.99 on the PlayStation 3 or 600 Wii Points on Wii.
According to publisher Activision Blizzard's press release, the free import offer will only be available to US gamers.
Guitar Hero: Warriors of Rock is due out in the UK on 24th September. Christian Donlan went hands-on in June.