It is probably a cross line inside the house. SBC or the Telco will only fix to the demarc line at the house; the homeowner is responsible for all inside wiring UNLESS they pay the monthly wiring insurance/fee. I suggest a line checker, found at electonic shack stores …. and fix the crossed line. One crossed line will effect all voice phones in the house, so it could be a tedious hunt ‘n check.
DSL and the high-pitch buzz