After solving all my ZB issues this year due to interference I am left on CH 11.
The one thing that bugs me is my ever-so-useful ST Arrival sensors will not re-join on ch 11; just dead.
I have a BLE gateway and tags on the way to solve that but I really like their simplicity and performance.
I have often been asked to try 25 but it seems a bit crowded up there according to the ZB scan.
The only strong signal that really bothers me is stronger than my hub. I have -65 to -56 and the unknown is pumping out -56 to -51.
There must be a ZB router in something I have but locating that would be a random guess.
I have 66 devices, all of which are just battery endpoints (except repeaters), water, motion, contact etc.
I can't see it being external to the house.
Any guesses as to what might be hiding this capability?
Does your power (or water/gas) company read your meter wirelessly? Those are often zigbee-based.
Ah, yes. Forgot about that. It was upgraded a few years back.
I guess I'll have to cut the tamper tag off and power it down to see. 
That sucks but you've probably nailed it.
A lazy Google says it's 902 and 928 MHz at 1 W so not in the ZB range.
I'll keep investigating as 1 W is a lot.
Edit: I'm in BC but Ontario says this so maybe we have their suppilers model:
Our Smart Metering system makes use of low power radiofrequency (RF) transmitters to communicate meter readings. Weak RF fields in the range of 2.4 GHz are produced during the system's normal operation.
Google AI, who can you trust 
BC Hydro smart meters use radio frequency (RF) wireless communications in the Industrial, Scientific and Medical (ISM) bands at frequencies from 902 MHz to 928 MHz.
OK, found the solution. Meter and model. Sad.
Home Area Network (HAN)
» Every OpenWay CENTRON meter includes a ZigBee radio
for interfacing with the HAN, in-home displays and load
control devices
» The OpenWay CENTRON can store consumption from 2.4GZ
OpenWay gas modules utilizing the ZigBee radio
