First thing to do when having this problem is to unplug everything except the DSL modem. Everything meaning all phones, answering machines, fax machines, satellite dish or digital cable systems, alarm systems..... Anything plugged into a phone jack.
Start with a standard plug in phone, not a cordless, with a filter attached, plug it in, and hit any one number to get rid of the dial tone. Listen. If it's clean go to the next jack. This will check all jacks.
If it's found to be in one jack, have that serviced or replaced.
If all jacks are clean then leave that one plugged in where it belongs. Now start with each additional phone and plug them in, one at a time each with a filter and check for the noise. If you still can't figure it out let the Tech check it out. If you do not have wire maintenance on your service you will be charged if the problem is found to be on the inside wiring. That could get expensive. Do you have an alarm system? DirecTV? Cable? Cordless phones? Computer modem? Fax machine? Water/Gas meter on a telco line? All need a filter on them. Could also be a defective jack?

With an alarm system you do need to have a separate line run for DSL. Alarms and DSL do not play nicely at all. Even if the alarm is not functional it still wreaks havoc on DSL. They use a special type of jack for the Alarm and I have never seen a filter for it. I think it is call a RJ38, but don't hold me to that.

FAQ by kadar