I am recording on a KORG D3200 with a SM7B mic, and am picking up RFI(radio/TV station interference.) Suggestions?
The sources and causes of RFI are numerous, enough so that there are entire books written on the subject.
As a place to start, go to the link below and use "RFI" as a search term:
Also, here are several papers on RFI causes and solutions:
Shure sells an in-line filter that might help: A15RF
Adding an isolation transformer at the input of the Korg might help: ProCo makes a 1:1 isolation transformer - model ITX.