Bob just asked the best question ... is the sound still present at the NTE with all else, including extension wiring, disconnected. You have answered yes to this, so that's good.
Did you report this as a noisy line fault or for the FTTC part ?
If as a noisy line, then don't be bothering the engineer with the whole SNR dipping thing .... they very likely won't be interested. Show a little interest yourself in the tests they run, ask if they don't mind you watching, if possible ask them to explain the results of the PQ (pair quality) test they run .... what you are looking for is a nice high AC balance, preferably over 60db (though the machine will pass it at 55db or over) and most importantly that both legs should be nice and balanced, ideally less than 3 nanofarad's difference between the two readings. The TDR function on their tester should be used to try and look for an HR ... also a good long listen to the quiet line test if the noise isn't immediately apparent.
If the engineers visit has been raised to look at the FTTC side of things, maybe an SFVA or a BOOST task, then
feel free to mention the SNR thing, they should be able to duplicate this with their tester in manual sync mode and watching the error counter and snr whilst they use the phone at the same time.