The utility box is not the RFI source, it is an egress point. Find the offending box and one of the houses connected to it is the RFI source.
A simple way to find the RFI house is to shut the AC power off (with the home owner's permission) to each house in turn. This may be faster and less intrusive than entering each house and sniffing with a receiver. When the RFI house is found, the AC power to each room is switched off one at a time to find the RFI room. When the RFI room is found, the AC power to each device is disconnected to find the RFI device.
OK, we've located the house that is the RFI Source. It is the one closest to the utility box. The signal strength of the offending interference is a bit higher at the home's electric meter (as compared to right next to the utility box).
Hopefully, I can follow your excellent above recommendations ... I'll report back on this in a few days.
thanks again! 73, Rich, K3VAT