What would cause a specific 2400mhz signal at a certain height and width through one window and nowhere else?

Measuring RF. I really don't understand this. We have a window that slides up and down in the front of the house. Around where the window has a ledge with locks you put the meter up against the window and the readings get high and there is a variable signal that does up to 2400mhz but as low as 1600mhz.  If you walk away from the window and keep the meter at the same height you can still pick it up but it gets weak. Is it the wifi for our router (x1 with hotspot turned off and wifi turned off) even though it has several layers of aluminum hvac tape along with a faraday net cage.. I went outside and got the reading on the outside but only when I place the meter up against the window and only in a specific spot. There is an alarm sensor but when I place the meter up to it I get nothing. Is this just an anomalous wifi signal moving in a weird way? I went out to the street with the meter and could not pick up this signal from any neighbors houses. Is this from a street light? Does xfinity hit your house with a continuous broadcast even if you have your wifi unplugged? Sorry for my ignorance with how wifi works.