Yeah was looking at the canopies, do they actually work? My mum doesn't have a router at her little bungalow so stumped. I'm thinking it could be feedback from the pylons or maybe the military out in the water checking for migrants. 

I've heard stuff about people picking up the sonar on land who are close by. Would make sense too with all these whales washing up on shore these days. 

never thought I'd be a conspiracy theorist believer. 

I'm having the exact same problem... staying with my mum in Cornwall (down from London)  as she is displaying corona virus like symptoms and now all I can hear in her bungalow is low frequency buzzing in my ears... cant sleep, stressed out and literally going crazy because of it... how can they do this to us!?