One of your old phones may have a leaky or shorted capacitor, thus putting a "ring-trip" on the line. Nothing to do with DSL. Disconnect all your phones, reconnect them one at a time, call from your cell phone, find out which one is causing the problem. If it happens when NONE of the phones is connected, the problem is in your inside wiring or the telephone company, and you would disconnect everything at the protector and test again to isolate.