Green Day appears to be up to its between-album side project antics once again, and this time, they're taking fans back to the 1960s.

Foxboro Hot Tubs

The veteran rockers, said to be working on the follow-up to 2005's acclaimed American Idiot, have reportedly posted six new songs online under the name Foxboro Hot Tubs. The songs are available as both streams and MP3 downloads.

The tracks are decidedly 1960s-oriented, with classic guitar hooks and retro melodies, but the trio's propulsive tempos and frontman Billie Joe Armstrong's signature voice are evident throughout. The six songs are called "Stop Drop and Roll," "Mother Mary," "Ruby Room," "Red Tide," "Highway 1," and "She's Not a Celebrity."

This is not the first time Green Day has secretly released new music as a side project. In 2003, the band put out an album called Money Money 2020 under the band name The Network. That sound was a mix of punk and new wave and all three members took on lead vocal duties.

Green Day is up for a Grammy Award in February, as its cover of John Lennon's "Working Class Hero," from the Instant Karma: The Amnesty International Campaign to Save Darfur, was nominated for Best Rock Performance by a Duo or Group With Vocals.