ARRGGHH! I know what you are going through. I had a radio transmission tower nearby (within a couple of miles) and had the same problem. When I switched from my forte full function preamp to a benz PP1 phono pre unit the Benz unit was sufficiently shielded that the fm was inaudible... then I moved to another location and never had the problem again. You may have to move to get rid of it or build a box out of mu-metal around your preamp!(very expensive)
