Using the 'Spectrum Analyzer' features built in to most APs and wireless clients will only show you other WiFi traffic not noise (almost always true). Also, they are not very portable. The earlier post about asking you local Ham Radio club is a good idea if there is anyone available and many Hams don't have equipment to listen to 2.4 or 5 GHz. You can search on google and other places for a 'usb wifi spectrum analyzer' for less than $50 that plugs in to your laptop. Be careful and read the specs though as some required that you use them in DOS mode. This will let you look at the actual received power level across the whole spectrum. You can walk around with a laptop until you find the noise source. It is still a steep price to pay for a one time fix.
If you are the crafty type you can get a ez430-RF2500 target board for $22 from Texas Instruments
. You will need to search for a software load that make it a SA but the are many instructions online.
If you don't want to roll your own and get a prebuilt solution you can use the Ubiquiti AirView2
for ~$40. This is a very nice tool. You could even split the cost with your neighbors or pool money or request the person with the noisy device foot the bill for finding it.