Finding Wireless Interference Source
If you were attempting the find the source of interference in a building what kind of equipment and utility programs would you use? The only time I have needed to do this was when a transformer exploded outside of my old place. That was obvious though because I didn't get any cell reception either.
Typically you would use a spectrum analyzer to look at the frequency range in question. Problem is most of them are expensive. We use a product from Ekahau when doing site surveys to determine wifi in use and interference from things like microwave ovens:
I believe we paid over $6000 for it though.
There was a cheap one out there that worked well I'll see if I can find it.
Other option is a software defined radio that can tune the 2.4GHz band, coupled with a radio program like SDR# (pronounced SDRSharp) that can scan the band in question. You look on the scan as its happening for peaks in the frequency range; those are either your wifi AP's or other devices causing interference. @gjacobse may have some info on one; the one I have doesn't go up that high in frequency.