had a '99 MB C43 that ticked also, this was normal - on the MB forums lots of back and forth how to quiet since some seemed to be valve noise, etc.

some of the owners switched oil to German Castrol and seemed to help, mine quieted a little on my C43 when I tried it... but shop foreman at MB dealer knew AMG engines and said the tick was normal - it was not really loud but very similar to what I hear in my SRT-6 now.