  The quantum indeterminacy caused by non-commutativity of observables at
different times sets a lower bound on the voltage noise power spectrum in any
conducting material. This bound is calculated explicitly in the case of
semiconductors with a conical energy-momentum dispersion of charge carriers. It
possesses all characteristic properties of 1/f noise. Its momentum
decomposition is found to be singular at zero particle momentum, a measurable
consequence being a sharp peak in the noise magnitude at small charge carrier
density. In application to monolayer graphene, this peak becomes M-shaped on
account of a continuous transition from the electron to hole conductivity. A
comparison with experimental data is made which demonstrates that the
calculated power spectrum is close in magnitude and congruent to the observed.
