Rattling sound from M54 330 engine at idle

Hi all,



There is a distinct and constant rattling sound at idle which I only noticed for the first time today.



Tensioner pulley previously replaced about two and a half years ago. Doesn't seem to be coming from the DISA box. It seems to come from the top or middle area of the engine itself. Failing water pump maybe?? What does a failing water pump sound like?



If anybody can provide some clues as to what this noise might be and how it can be resolved it would be greatly appreciated!



Thanks in advance.



http://ift.tt/1A7ukcl