Hi. My design requires that the output of a high voltage DC-DC converter is low noise (within 20 mV pk pk up to 20 MHz). My TOP255HX based supply provides the DC input for the DC-DC converter. The DC-DC noise is well suppressed with filtering, but the switching noise from the PI based circuit is appearing on the output (50 mV pk pk). Total power is around 12 W. Input 115VAC 60 Hz. When I place a low value capacitor (20 pF) between the D and S of the transformer, it is reduced some. Can you provide some general info of some other things to try further reduce this noise? I am curious about shielding or other circuit techniques. Note that chassis ground is isolated from the output return. Schematic and transformer info and layout attached. thanks!