A170 cdi knocking noise

[gray11]

Hi all, ive had my w reg A170cdi for about 6 weeks and it was running
fine until 2 days ago when the engine started making a knocking noise on
tickover. this has got louder but as soon as the car is revved or driven it sounds fine. ive checked the pulleys and they seem fine. it was serviced approx 4000 miles ago and all fluid levels are fine and no obvious leaks.
has anyone got any ideas of what to check next ?

 

[Kyliewww]

Has it just started with the colder weather?

 

[gray11]

yeah it started about 2 days ago, its only on tick over though and the car drives fine otherwise.

 

[WG M-B]

Injector spray pattern?

 

[Kyliewww]

Does the W168 have an aux' heater? As soon as it gets cold, my 169 makes a terrible noise on tick over but I get instant warm air.

 

[gray11]

what would be wrong with the injector spray pattern ?
i dont think it has aux heater.
i have noticed that if i try to pull away gently the car judders but if i pull away hard its fine. its a clutchless manual (not sure what this transmission is called).