|When we had dsl the same problem would present itself every 6 months or so. It was always the phone line.|
Either the cord from the modem to the wall jack needed to be replaced or a connection in the attic needed to be tightened.
Try plugging your phone into the dsl line and see if you hear any static....if you do than thats the problem,
Also...and I have no idea why but the connection on the back of the computer would get dust in it. How dust can get into a phone jack I don't know except the fan on our system pulls air in not out...
Somewhere a connection isn't 100 percent.