Concrete runways with rebar interference
We had a case of interference on 2 channels (54 & 55 IIRC) at our flying site several years ago. The source was found to be a pager repeater station that had drifted out of alignment. One of our members who knows way more about this stuff than I do tracked it down, compiled evidence of the interference, and met with the owners of the station. They confirmed his findngs and recalibrated their equipment.
Gordon