Switching noise of TNY280 coupling into transformer secondary

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I am currently having a noise issue with a board I'm trying to debug. 

The switching noise of the TNY280 is coupling into the waveform on the transformer secondary, which I assume is expected.

However, I then try to filter that noise out on the transformer secondary with an RC filter before it goes to my voltage feedback circuit, but

then the coupled switching noise doesn't seem to get filtered or decrease in amplitude at all.

I believe I have a proper layout for the TNY280 (see pic attached for a quick shot), but would you know why this would occur?  I do have ground fill everywhere around the part, instead of just soldermask.  Would that cause issues related to this?..

Thanks.

 

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