As my earlier note I replaced my fuel filters, (2) which were black as the ace of spades, I don't think they have ever been changed, they are easily forgotten when they are on the underneath of the car. The car now is running a lot smoother as Victor suggested however due to my current discharge/battery issues I have not had the chance to give the car a long run but since changing the filters I have not heard the noise.
For those DIY'ers out there the job is quite straight, i put the front of the car on ramps to improve access, put bowl under the filter, undo the phillips screw and drain casing into bowl, with 27mm socket loosen both filters and drain excess into bowl, lubricate the o-ring seals on new filters, fit new filters torque to number on case, refit phillips screw then I turned the ignition on about 10 times to bleed the filter before starting the car.
Be wary in 2012 they swapped filter type so best remove one of the filters and measure length and diameter before ordering. I bought the wrong ones initially which were pleated, the right ones for my car have a smooth filter media. Richy