A lot of DSL modems actually have routing functionality that interferes with your actual router. They tend to use a PPOE setup, which means you have to tell your modem to not do PPOE and use the settings that it had to tell your router it's a PPOE connection, complete with the login user/pass and external IP address the modem was getting. I know that sounds complex, so maybe just google on that subject with some keywords and you'll likely find the steps for it.
I have walked around with my network discovery tool.No other wireless networks in the area. And we're low tech. No Cell phones no cordless phones in the house. One of our phones actually has a dial on it And it's pretty far away from the microwave.