Are there more houses in the area? Any new businesses?
If there are more houses, that means more electricity and that means more static and magnetic interference. It could also be more wireless alarm systems, new wireless gaming(Wii, PS3/4,etc) and WIFI jamming up the airwaved
New businesses means the same thing but, more so. More florescent lighting(more magnetic fields), more video security(transmitting to a monitoring site) and more electricity(again, more or stronger magnetic fields).
These are all things you didn't really need to worry about a few years back