There is an RFI modification for Microkeyer II's below SN 765 that might
"Those who are experiencing RFI in the microphone circuit can add
bypassing in the field by installing a 0.001 - 0.01uF high voltage
capacitor (the value in not critical) from the shield of the USB
connector to the metal mounting bracket of the DB37 connector as shown
I do not own any of these products.
RFI mailing list