What does this noise mean

Hi my car has just turned two hundred thousand miles last Friday and running well,but then out of the blue can this very loud noise no noticable loss in power,no additional smoke just this loud banging noise it sounded like it was coming from the air fitter area,it still starts first time and runs,iam not driving it. I have had the RAC out,and her told me it was an injector problem or turbo problem, i have had starting problems before and this was an injector gone totally different symptoms. Would you be able to help.
Thanks