They're second major label album "Dirty" mistaken to be grunge influenced, but listening to earlier albums and seeing how they had developed, it's not very grunge at all. The early 90's era of their music saw them with a much more stripped down sound, however without leaving their noisey delivery and aesthetics. "Goo" and "Dirty" probably they're most popular albums, are very unlike their other albums, the bands general sound is much more noisy, experimental and jammy.
Sonic Youth took the very foundations of rock music and abandoned them, they re-defined the structure. They were really more punk influenced than rock, I hear more contemparies Husker du in there sound even The Velvet Underground. But what Sonic Youth had was even more experimental, a sound more about texture and layers than the tune or melody. Walls of sound if you might. This would later influence bands like "The Jesus And Mary Chain" and later "My Bloody Valentine" and they further built on this. They were even a key influence in "post-rock", with the "Washing Machine" albums ender "The Diamond Sea" and later album "A Thousand Leaves".
But now in 2010 I can hear their influence everywhere, the growing noise rock scene with bands such as "No-Age", "Lovvers", or "Wavves" all sound fairly Sonic Youth-esque. Though now there are even more far out experimental bands out there, they owe some debt to Sonic Youth and they're different outlook on noise and song structure.
