ghost noise

[twisted spanner]

Hi my 2011 Astra J 1.7 CDTI has a strange noise that is getting more and more frequent, when i accelerate away and dip the clutch to change gear, there is a ghostly noise that starts off quiet and gets louder, it got worse when i changed the fuel filter, but then became less common for almost a year, but has now come back with a vengeance. I almost think it could be to do with fuel pressure?
Just wondered if anyone else had experienced this and how they got rid of it. The car itself drives fine with no issues at all