Rocks is the fourth studio album by American rock band Aerosmith, released in May 1976. AllMusic described Rocks as having “captured Aerosmith at their most raw and rocking.” The band began work on the album by backing the Record Plant’s mobile recording truck into their rehearsal space, named the Wherehouse, in February and March 1976.
A tape containing an early version of the Rocks tracks as instrumentals leaked online around 2010. Mark Prado, Aerosmith: Tapes From The Cellar reviews the recordings as:
The music for the album is just about complete here, but there are zero vocals. Tyler was known for delivering his lyrics as the last element of the album after the music was nearly done.
Mark Prado, Aerosmith: Tapes From The Cellar
What we have here appears to be exactly that: almost finished music that Tyler then put lyrics to, which then allowed the guitar players to add leads.
Without the leads, the songs’ rhythms are emphasized and really stand out, such as on “Nobody’s Faul”, which features a more proper ending here, instead of a fade as heard on “Rocks”.
“Rats in the Cellar” features a vocal count-in to launch it. The beginning of the track is just the rhythm guitar, so we don’t hear the “answer” that the later lead would supply.
A guitar solo does appear on “Home Tonight”, but not the one that would be on the final version. Tyler can be heard scatting in the distance as the track comes to a close.
“Last Child” is fairly well-formed, but is missing guitar parts, including Whitford’s lead.
“Back in the Saddle” does not have its ending yet; it fades out here and is missing all its signature aural accoutrements: vocals, spurs and whip sounds.
“Combination” has a couple of yelps not heard on the final version, likely from Tyler.
The session is an interesting document without the vocals, which, when added later, would make these iconic Aerosmith songs.
It is known that the 70’s session didn’t have proper outtakes, but rather simple shells of song ideas, chord progressions and melodies; such could have been the case of “Uncle Tom’s Cabin” and “Tit for Tat”.
A different review of the bootleg reads:
The world’s first appearance soundboard sound source is once again emerged from ZODIAC label! Completely unreleased studio sessions Tracks of the highest masterpiece album “ROCKS” to the maximum of hits for Aerosmith in the 1970s. Its contents are the eight songs of the album, except for Sick As A Dog, is what the band is playing session with vocal without Steven Tyler. And twice I was surprised because the sound quality is the official-class stereo soundboard! Of complete brink of music, good meaning in rough playing (Home Tonight except guitar solo does not contain), and exerts complete all the songs from the intro to last (with fade-out part), rough vocals without also I enjoy as a mix version. Of course, because the over-dubbing, such as the official final version has not been applied at all, the taste of the last band sound itself. This is irresistible anyway. I can listen also to little conversation and before the start of the human voice count in between songs.
The Back-Burner: Aerosmith Outtakes & Demos 