  We calculate the low-frequency current noise for AC biased mesoscopic chaotic
cavities and diffusive wires. Contrary to what happens for the admittance, the
frequency dispersion is not dominated by the electric response time (the "RC"
time of the circuit), but by the time that electrons need to diffuse through
the structure (dwell time or diffusion time). Frequency dispersion of noise
stems from fluctuations of the Fermi distribution function that preserve charge
neutrality. Our predictions can be verified with present experimental
technology.
