Human intracranial microwire recordings often have signal-to-noise ratios (SNR) below 10 dB. The physiological signal amplitude is fixed, thus, SNR must be improved by reducing noise. This reduction requires an understanding of noise sources, coupling mechanisms, and their relative magnitudes. Electrical interference measurements were made using typical impedance mismatches (100 kilohms) to measure capacitive coupling and typical loop area mismatches (30 centimeters squared) to measure magnetic coupling. Sources considered were: power lines, fluorescent lights, radio transmitters, and non-power line interference. Capacitive coupling to power lines (11.4 microvolts root-mean-squared) and fluorescent lights (9.7 microvolts root-mean-squared), and a clinically required series protection resistor (4.2 microvolts root-mean-squared) are the greatest sources of noise, but many sources have magnitudes which could contribute significantly detrimental noise power. These relative magnitudes show the most beneficial sources to eliminate. Additionally, the preliminary version of the above noise measurements were used to design a new intracranial recording system.