My friend at school has an Audi GT Coupe '86 with the 5 cylinder.  He says
that in the manual it states something like "some intermitant lifter tapping
does not necessarily indicate engine wear".  In other words, somehow it is
normal for that motor.  His has it and he used some Marvel Mystery Oil with
his oil change and it quieted it right down.  The next oil change he didn't
use it and the noise came back.  But that motor has some power (my buddy has
so many tickets and I never knew why until I drove that car myself.  Vroom!!)
Happy trails
Ken Wilford
John 3:16