1. A circuit for automatically selecting a low noise frequency for use in a device comprising: a plurality of sense channels, each sense channel configured to receive a signal; a summing circuit coupled to the sense channels and configured to generate a sum of the signals; a pair of magnitude circuits coupled to the summing circuit, one of the pair coupled to the summing circuit through a first mixer configured for demodulation with an in-phase (I) component of a demodulation frequency so as to calculate an in-phase magnitude value corresponding an amount of noise at the demodulation frequency, and the other of the pair coupled to the summing circuit through a second mixer configured for demodulation with a quadrature (Q) component of the demodulation frequency so as to calculate a quadrature magnitude value corresponding to the amount of noise at the demodulation frequency; and frequency selection logic coupled to the calculation circuits and configured to select without intervention from a processor the demodulation frequency as a low noise frequency if the amount of noise is low.