Thanks for the replies chaps,
I don't have the ECM XLR connections but when we tested the newer CS3e we used the same cables/TX unit and the newer mic didn't suffer from any RF, which leads me to believe there is a fault on the mic somewhere.
My Mic is below the 2791 serial number, but I have done the mod and there was no difference, again leading me to believe there is a fault on the mic.