You don`t say what noise you are hearing or if you have had a code reader onto it but you could check for any splits/cracks in your intake system,pay attention to intercooler hoses,also try removing the intake pipe to your turbo and check for play in the impeller and it is spinning freely,I would have thought if you had problems with your air flow meter/egr valve that faults would be registered and lights would be showing,I am hearing of a lot of problems just now with cheap supermarket fuel causing problems with filters etc and that is from the RAC drivers who come into my work now and again but would start with the previous checks and see how you get on. Good luck.
cdc
February 2015
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