My WiFi signal strength is all over the place. I'm not moving

I’m trying to debug WiFi problems in my house.
Sitting in a room where I have intermittent problems, I fire up InSSIDer.
I’m about equidistant from two APs, and further from a third.


My signal strength is all over the place! This plot vs time is me sitting in one spot!

Any hints what I should be looking for, to explain and fix this?