hi mate, Firstly I over haul Delphi Common rail injectors for a living, if they have been done correctly you should have brand new codes , but if you haven't they have not been done properly, they have to be ut through a long and thorough test on a specific bench which costs 40k , they need to be recoded using ids software, this will fine tune each injector to get the best out of them i.e fuel economy performace , and sometimes can stop engines running rough and smoke etc, as for the buzzing sound if its coming froim the rocker cover area it will be the valve in the injector that's 2mm in dimension and moves micron in mili seconds its miving that fast it makes a sound like a duck . I would take your injectors out again and send them to Colchester fuel injection ltd where I work cheers