Is the interference coming from a radio station or is it heard on the AM mode? I had problems with Power line noise from 40M thru 6M here on a few occasions. There is a free program called sound card O'Scope. It will allow you to take Pictures of the interference and also record it. Mark the date and time of the offense and send copies to the station and the FCC. I made many calls to the power company and got nowhere till I did pictures and recordings. I now have the email of the head technician and a "special" number to call for a job ticket start.
