Fiat Scudo Van engine making tappet noise randomly?

On my way home tonight my fiat scudo van started making a noise from the engine which sounded like one of the tappets knocking, I crept home but by the time i got home it had stopped. I checked oil and water, all is fine, it is a 1.9 diesel with apprx 105.000 on the clock, any suggestions? (Noise lasted about 10 mins)