My 2001 Citroen Picasso 1.8 SX petrol has started making a rattling/ticking noise that sounds a it like a diesel. I can hear it when idling and it seems to increase in speed as I accelerate. 
 
The car runs as usual in all other respects. 
 
Any ideas what the cause may be? Is this something I should get looked at urgently? 
 
Thanks 
 
Chris
                            
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