I have been monitoring my SNR using RouterStats and I have noticed that I get a sudden drop in SNR around this time. The graph is below. By the way, I know the SNR only started at 5dB, but the sudden drop must mean some cross talk or some other noise on the line, surely?
Probably an example of SHINE - single isolated impulse noise The Exchange DSLAM is told to ignore these under its "blip logic" - unless there are lots of them,at which point it is no longer SHINE but REIN (repetitive electric impulse noise). My guess is someone switched something somewhere and this gave off an impulse which was picked up by your line. Perhaps even in the next door house and it was picked up by the part of your line than runs overhead from your house to the pole - as a possibility - in short who knows! Technically speaking cross talk is interference only arising from the operation of another transmission system. Usually this will be from other telephone pairs in the bundle of 200+ lines that make up a physical cable. This might have been a cross talk impulse or an radio frequency impulse picked up by your line.