take the sepentine belt off or if you don't have the serpentine belt take off belt to air pump and start up the car and see if noise stops.only run it for a short time if there is no noise then it is not timing chain. it may be the air pump cycling when you first start up. just put a timing chain on my 91 300 sel because of rattle on startup, turned out to be air pump. but my car has 175000 miles so it didn't hurt to do it plus i did it myself. parts where only 100.00. plus the bearing on my fan clutch was making noise taking off belt is how i isolated this problem. with the serpentine belt it makes it hard to isolate individual parts.hope this will send you in right direction.