Strange Phone Line Issue

["ABLE_1" <royboynospam@xxxxxxxxxxxxx>]

Had a strange occurrence today with a customers phone line that is still
un-resolved.  Thought I would share and see if anyone has any hints as to
what's going on.

Customer has one phone line.
Standard set up with RJ31X.
Phone line has DSL
DSL Filters installed.
System Communicates Signals to CS, all good
Normal phones in house with Answering Machine and CID Box
Previous connection for UpDownload OK.

Problem comes up when I try to connect to panel remotely.  Panel will hang
and then disconnect.  Went to site today and used my laptop to connect to
the panel thru my "private phone company in a box" which would be the same
as connecting over the phone line.  Connection is good and data transferred
as it should.

Connected my Butt Set to the phone line and dialed with my cell phone to
trigger the panel to answer, Answering Machine Bypass function enabled.
While listening to the amplified speaker I heard what sounded like a modem
answering with a carrier tone after the first ring.

To bring this narrative ahead a bit, I ended up at the demarc and with the
house, panel and all disconnected so that I was connected direct from the CO
and the following was observed.

On the speaker of the butt set just before the 1st ring a small buzz click
was heard and then after the first ring a carrier tone is heard for about 1
second and then a pause and then the next ring.  Nothing else is heard
except for normal rings after that.

It is as if another modem or panel is on the line and connecting on the
first ring but not answering the call.

Has anyone experienced anything like this and/or what the blazes is it or
could it be?????????   I ran out of time to investigate it further on site
with voltages, current, etc. but it seems very strange.  Any thoughts from
the masses would be welcome.

Thanks,

Les