There are three types of intrinsic noise: Johnson noise, shot noise, and 1/f. Johnson noise is the result of thermal fluctuations. The rms Johnson voltage noise is:
Where k is Boltzmann's constant, T is temperature, R is the resistance of the sample, and is the bandwidth.
When a current is passed through a material, shot noise occurs. It is only seen when electron flow is uncorrelated so is usually not visible in a metallic system.
1/f noise is usually mysterious, associated often with semi conductors in instruments, and intrinsic.