Car Alarms
A while ago, a Wi-Spy user posted on our forum about a strange source of interference, which he discovered was coming from a parked Mazda 6 outside of his house.
You can read it here. http://metageek.net/forum/wi-spy/mazda-6-car-alarm
Note:
He wasn't using Chanalyzer for the recording, he used one of the third party applications called Eakiu.