new type master noise/vibration

Hi, my 2010 master was back at the dealers recently for a recall, fap filter pipe replacement, since this has been done the van has developed a noise/vibration, most prominent at around 55 to 60 mph, almost sounds like a wheel or tyre out of balance, but there is no feel of anything through the steering wheel, new tyres and balanced, no uneven feel through brake pedal, feels like something is out of balance within the engine, if I depress clutch pedal slightly wheen driving I can feel pulsing through it, I have had it back to the dealers twice as the noise/vibration was not there before recall work, they cant find where its coming from

unless they do a total strip and rebuild they also claim the clutch pedal feeling is normal, there is 30'000 miles on the van and has been pretty much flawless until this, anyone's help and suggestions would be greatly appreciated,