Many electron theory of 1/f-noise in hopping conductivity
  We show that $1/f$-noise in the variable range hopping regime is related to transitions of many-electrons clusters (fluctuators) between two almost degenerate states. Giant fluctuation times necessary for $1/f$-noise are provided by slow rate of simultaneous tunneling of many localized electrons and by large activation barriers for their consecutive rearrangements. The Hooge constant steeply grows with decreasing temperature because it is easier to find a slow fluctuator at lower temperatures. Our conclusions qualitatively agree with the low temperature observations of $1/f$-noise in p-type silicon and GaAs. 
A. L. Burin, B. I. Shklovskii, V. I. Kozub, Y. M. Galperin, V. Vinokur