!992 SC300, 145K miles. Recent timing belt and water pump. Have been getting brief clatter(like a timing chain) at cold startup. Any ideas where to look?

 

Check you radiator fan and see if it is woobling. I have the same problem on my LS400 and it turned out to be the fan pulley assembly. It a real pain to get at it. I turned out to be the bearing went bad. It finally starting making noise all the time. I thought it was the water pump, but looking at the fan spin you could see it was the fan pulley assembly.