I do not know about PWM sensors, but I am using the cousin, a l/f (luminosity to frequency) converter. I have zero noise problems beyond the obvious that measuring the frequency in a timeslot gives a jitter of 1 for constant luminosity. This is without ANY shielding, optoisolators, or anything else, just a schmitt trigger input and works beautifully in a very noisy environment (same mount as a 55A switcher).

Erik