I,ve recently purchased a yr 2000 2.7 d ML. I have noticed when I put my foot down on the gas a Hissing/ whooshing noise comes from the left front side of the engine. The noise tails of when Cruising. The car was returned to the garage for checks and the mechanic ( not merc experianced) was a bit puzzled and could not find any cause. He seemed to think it might be a normal function. I would gratefull for any assistance. Its my first Merc im a BMW convert.