Can't hurt to try but they aren't hydraulic lifters, they are however adjustable if you remove the rocker cover.
typical causes of noisey tappets include:
Bent pushrods
Weak or broken valve springs
bent valve stems or stickey valves
excessive wear in cam followers or cam lobes (moreso on hydraulic lifters)
bent or broken rocker shaft
also on the TDi the bronze cam followers can also break
does it run smoothley, is it using too much fuel? if not then chances are the valves are closing properly, start by checking the clearnece in any case.
