If you have a laptop and you can somehow battery power your Flex then direct cable them. IE lan goes from PC directly to Flex. Some people have managed to use a WiFi access point on battery so they can carry the laptop around.
Now unplug EVERYTHING in the house until you find the thing (or things) that start to cause interference.
If you go battery and unplug everything and it is still there then it is from a nearby source not within your house.
I did this exercise myself and only got part way through it because there were TONS of things plugged in and I just ran out of time.
1. Does the noise occur 24/7 or only at certain times of the day? (Street lights and advertising signs come on at night, while noise from solar panels will occur during daytime hours).
2. Are there any street lights in your neighborhood that aren’t working and appear to constantly cycle or “flicker”?
3. Does it occur on multiple bands or only one specific frequency?
4. Is it a repetitive noise, a signal that seems to appear at evenly spaced intervals, say every 100 khz?
5. Is it visible when the antenna is disconnected?
6. Is the noise present when all household circuits, except that which supplies power to the radio area, is turned off?
7. Is it possible to temporarily shut off power to the radio area and obtain power from another circuit? When doing so, is the signal still present?
8. Does the noise seem to decrease or completely go away when it rains? This usually indicated bad HV insulators on a nearby power pole.
9. Is it visible on multiple antennas? How about on a simple indoor antenna?
10. Is it visible when the Flex Radio is connected to another PC, one not normally used?
11. Is it visible when the Internet service is temporarily disabled (including all wireless devices, switches and hubs?)
12. Can the noise be received on another conventional analog receiver?
13. Using a yagi, even a tri-band yagi, can the source of the signal be seen to increase in one general direction?
14. Has a neighbor recently had a new Internet service installed?