I apologize in advance for boring any gearheads who know about this already, but it was quite a surprise to me!
At a client's home, I connected my laptop to a phone line for dial-up where the very MOMENT that the modem started to look for dial tone, there was noise on the line that sounded like an already-connected modem. Worse, two other computers in the house had the same problem, and had had the problem for about five days. This noise got in the way of the computer going online at speeds more than 4800 baud (is it baud?), and the computer usually disconnected within a couple of minutes.
DSL had been present on this phone line previously, but because of the way sbc (used to be Pacific Bell; "sbc" is supposed to keep us from knowing that it had something to do with Southwestern Bell) does their procedures, service had to be cancelled, disconnected, and reordered to change the name on the account.
The phone company people at 611 had no clue what was happening, but were willing to devote more than an hour to talk about it. The nice people in India, working for the DSL division of sbc, had no clue what was happening and suggested that I call 611 locally. Or maybe call the DSL division back during office hours. And it took them about two hours to say that.
I finally started looking at things that should not need looking at, only to find that the telephone set wiring did not have a DSL filter. The home setup was supposed to be ONE DSL filter between the phone line and ALL of the telephones, as only one phone was usually used at a time. But nobody had followed instructions and installed the filter. For some reason, nobody ever heard any funny noises on the phones, prompting them to wonder if the filter were in place. As long as everybody used the DSL through the LAN, no dial-up modem had ever been connected to the line.
And apparently, the phone company electrically reconnected the DSL signal the very same day that the service was reordered, even though the promised due date was some ten days away. And we could not hear on the regular phones that DSL was there.
So it seems that if a dial-up modem sees a DSL signal, it will somehow do something to the DSL signal that results in noise in audible frequencies, like a hissing sound, that TOTALLY gets in the way of using the computer in dial-up mode.
This is, of course, a totally unexpected scenario, but it is the kind of thing that continually reinspires the phrase,"that is why it is called CUSTOM."
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