Your description pretty well describes The Danglers: http://thedanglers.bandcamp.com/
Violin, Upright Bass and Drums (mainly that, some guitar and keyboard over the years too). Amplified and distorted as if in a hard rock / metal band. Plays stuff from Slayer to King Crimson to Coltrane.
Not all of their stuff is posted up on that page, but it's a lot of it. Look through the discography on the right side. Each song is unique, and the sound evolves over the years across the albums, so don't think that if you hear one song all the rest of the stuff sounds like that.
If you want to hear stuff that's more towards the freeform side of that group click on the album "Backpages". But there are certainly elements of all you asked for (freeform, improvisational, distorted shredding) throughout all the stuff.