Noise is so hard to trace and ultimately can you expect BT to actually spend possibly days searching for a source they are unable to control?
Have you tried a different modem and PSU?
You might find that the modem/router is overloading itself, then the power regulator starts playing up and suddenly there is noise! A resync may also have a soft reset too ...
Can you borrow an other modem/router? Possibly one which allows you to capture various parameters over time.
M H C
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