Occasional RF Interference @ our field
See if you can locate a ham radio club in your area. They might be registered with the local sheriff's office in case emergencies arise when extra communications facilities are needed. Some of the new ham transceivers have 'panoramic' viewers that show activity around a given frequency of interest. Maybe they can dial in your R/C frequency and monitor the activity in the surrounding bandspace and look for a pattern and maybe can decide if it is speech or digital transmissions that are the source and if there is indeed a pattern to the times it occurs. Quite possibly hams in the area already know of a known source of interference in the area. They may have been falsely accused of creating it in the past!!!