I seem to recall that some EU's 'Caller Displays' were polarity conscious. Upon migrating to ADSL from PSTN, the reversal of the polarity caused by the subsequent Exchange 'Jumpering' (Running of wires), a few CD's stopped working until the wiring was swopped around.
If you have been 'messing' with the wiring, this
may be the issue ??
PS ..... for info ...... what you can hear upon receipt of a 1571 message is officially called 'Broken Dial Tone'.