One wireless router and two wireless access points. Have tried both 2.4Ghz (different channels) and 5Ghz. Even at a distance of only 1 meter from the router, there is significant interference every 10 seconds causing 1000-2000 ms roundtrips when pinging or packet loss. Otherwise the roundtrip times are 2-3 ms.
The interference appears across the entire house. Have tried shutting down electrical equipment but to no avail. Have tried all ethernet cabling in the house and there is no problem with interference over the wired connections.
I have updated router firmwares, increased and decreased transmission signal strengths, tried to run only one router at a time etc. Network is limited to only 802.11n/ac to prevent issues with older devices, and firewall is disabled.
What could the cause be, since it hits both frequency bands at the same time hard? A radio transmitter in the area? Interference caused by high currents?