I'm seeing this interference on channels 4-8 and WiFi is not working, most of the channels are jammed with 98% utilization. It seems to be a device that sends/emits for ~20seconds and stops for ~10s. But I haven't been able to identify what it is.
I had a problem like that one and was lucky to discover the source was a point to point wireless bridge someone had installed and thought they were being smart by using non standard channels like 5 or 8 or something to avoid interference..
I recognize I was very lucky to discover the source easily. I have heard of people renting or purchasing scanning gear and knocking on doors to try to find interference sources.. Very time and $ intensive.
Can you just use channel 11? That looks pretty clean for now.