Thanks for all the good suggestions! To restate: (1) car has a brand new timing chain and upper guides; (2) New timing chain tensioner put on 10K miles ago; (3) new motor mounts just installed (found one broken mount but new motor mounts made no difference); all lifters tested good; since noise comes from passenger side front of engine by cylinder No. 1; new lifters for cylinder 1 installed that made NO difference. Using Castrol GTX 20-50 now upon suggestion of indie mechanic; used to run diesel Rotella 10-40 and seemed to quiet it down a little. How do I test for camshaft play? maybe there is some camshaft "float"? some bushing somewhere? all cam towers torqued to specs with NO difference. Car has been running with this clacking noise since I acquired at 93K miles; now shows 125K with no ill effects other than it is bothersome to hear the noise and I want to solve the problem.!