I report them to Thames Water [www2.thameswater.co.uk
Enter your postcode and you will be taken to a page where you can report noisy manhole covers .
In a road like Barry Road Thames Water will say they have to liaise with Southwark about directing traffic . Then after many many months cones will appear and signs indicating that Thames Water will be working .
Nothing will happen and the cones will be removed .
After many many months a few shovel fulls of tarmac will be thrown over the manhole cover from a passing truck .
Sometimes the tarmac will set and remain on the cover deadening the noise . More often , as passing traffic drives over the soft tarmac it will be broken up and spread across the road .At which point you start over with Thames Water .