Design your circuit board and its enclosure such that the diodes stay at the lowest temperature possible. Use vents in the enclosure and fans if necessary. Also don't place electronic components, such as power transistors and high-wattage resistors that dissipate excessive heat, next to the diode circuits. Remember that the higher the operating temperature, the higher the noise level.
Connect capacitors, known as bypass capacitors between the diode's anode and ground and between the diode's cathode and ground. Experiment with different values of capacitors to determine the effect on the noise voltage levels on the diode's cathode. Use high values of capacitors in the microFarad range to filter out low frequency and mid-range frequency noise. Use capacitors in the picoFarad range to filter out high-frequency noise.
Connect bypass capacitors on the power supply connections on the printed circuit board to filter out noise spikes caused by switching diodes. Use high values of capacitors in the microFarad range if the diodes in your circuit are switching at low and mid-range frequencies. Use capacitors in the picoFarad range if the diodes in your circuit are switching at high frequencies.