Tappet sort of noise

[mauricio]

I was driving on the Hume hwy recently and noticed that I have this type of noisy tappet (tap, tap, tap) sound occuring at 100Km speeds. I turned down the radio, it was still there. I changed the box from drive to manual, it was still there. Anyone else have this type of issue? Car is a 2009 TDCi MB Mondeo with about 125,000Km on the Odometer. It's intermittent but it's starting to occur a little more frequently with no real triggers or types of driving conditions to narrow down. Cheers