Debugging noise on broadband signal

[#1]

A site I sometimes visit suffers from huge noise spikes on the broadband signal that seem to go on day and night and appear to be getting worse.  The target SNR must be 15 dB and even that is not enough to prevent frequent disconnects.  Any thoughts about how to cure or ameliorate a problem like this?  By the way the ISP is Demon so this is not a Plusnet issue.

[#2]

If that's not a faulty line, and audible noise should be evident if it was, and you've ruled out the modem/router and filter by trying substitutes in the test socket to eliminate internal wiring problems, then it's either RFI, LineCard or a tie-pair problem.
Make sure you've done the obvious checks and then try wandering around with an AM radio and see if there's anything local generating RFI.
Switch off the monitor whilst RouterStats is running in case it's the monitor power supplies causing the problem, leave it for a little while, switch on again and see what happened to the graph. Try and alternative computer in case it's the PC power supply.

[#3]

Quote from: Anotherone

... try wandering around with an AM radio and see if there's anything local generating RFI.

Tuned to any particular wavelength?

[#4]

Usual recommendation is around 600kHz (simply because it's the middle of the ADSL(1) band - not on a frequency with a strong radio station. But it depends what (if anything) is generating the interference that's disrupting the broadband. Once you can identify the "sound" of the signal which will come on go with what you see on the SNRM graph coming and going then you tune to where you can get the strongest signal for that, which then enables better tracking.