Citroen C5 tapping noise

[Danbuoy]

Hi, I have a 58 C5 2.0 HDI, done just over 36k. Noticed this morning there is what I can only describe as a constant tapping noise which seems to be coming from the engine. Can mainly hear it when stationary. Don't know if it is doing it at high speed, as I can't hear it, but at very low speed (10mph and below) I can just about hear it. Noise sounds a bit like popcorn popping in the microwave, thats how frequent the noises are. Car feels fine to drive, but just at a total loss as to what the noise could be. Seem also to be able to feel it through the clutch pedal.

[SwissSPEC]

If its a piston sounding noise, then it may be the crank pulley (the one which has the bearings)? Can't remember if i felt anything through the pedal or not though, mine's a mk1 c5 2.0 hdi 110bhp, so your issue may be totally different. Probably best taking the car to an indie to see if a bigger problem is looming on the horizon if you leave it.