Knocking Noise

I have a 53 plate pre-facelift FL1 Td4 and had a knocking noise when warmed up and idling. I was told it would be the crankshaft pulley so I bought a BritPart one and had it fitted. It eased the noise but very quickly returned.
Does anyone have an idea what it might be? I have it booked in but if it’s something g I can do diy I would rather buy and fit things.
Thank you.

Britpart provide various versions of their parts. If you bought the cheapest version then it may well have failed already, on the other hand it might be something else.
Don't forget to get your money back if the part has failed.

Thank you. I will have to get an opinion from a mechanic as I am to new to diagnosing and so forth to know. It has been suggested that it may be one of the two tensioners so I will have to wait and get a report.

Let us know the outcome to help others.

I definitely will do. The car is booked in on the 15th July so I will know then.