Landline Problem

Our landline has a buzzing sound on both incoming and outgoing calls.  I have checked all in home connections, wiring, etc. with no success.  AT&T box on side of home supposedly has a 'test jack' for a landline phone but it is not present in the box AT&T installed.  Is anyone else having a problem with a buzzing sound with their landline?  The internet says this is a common problem with AT&T over time.  Any suggestions are welcomed.