id heard before you can strip and clean the hydraulic tappets found on most later vw's , its nearly always the reason they tick
1, take your tappet and slam it onto some wood as hard as you can , might take a few goes for the center to fall out
2, work over a sheet of white paper as the parts are tiny , the small cap on the left simply pops off with some pliers to reveal a spring and a ball bearing , take some time to clean all this up and reassemble with some clean engine oil , the center take a good shove to click back in place