Amazing uses feedback and pedal noise to create a test pattern sound.

Geiger sounds like a motorcycle and a Geiger counter, at the same time.

Siren uses feedback to simulate an air raid siren behind simple chords.

Headstock sounds like bongo drums but what's that other sound?

Nocturnal resembles nothing in particular but has a jazz flavour.
 

Butterflies & Zebras have literally thousands of interesting and unreleased sounds.