I had a Panasonic 2.4Ghz jamming device. Could take out channels 1-11 all at the same time. It wasn't supposed to be a jamming device, it was supposed to be a cordless phone. Setup wifi for a customer, and it worked fine when I was on site. Later the customer complained it was completely unusable, in what they thought was a random fashion.
Turned out whenever they used the cordless it pretty much made so much noise on the 2.4G frequence wifi wouldn't work. Phone itself worked fine. Had them get new phones and the problem went away.