replace the cam and lifters. no additive is gonna replace the worn metal that is now missing. so you will be a slave to this until it finally goes beyond what any additive can do. their is no substitute for metal. if additives are that good, they would come from the factory that way to begin with.
however, this trick is used very commonly to quiet the motor down long enuf to sell your problem to someone else!
what i would do i put a bottle of automatic trasmission fluid in the oil fill.
The reason behind this is because your car has hydralic lifers so you can't adjust them, so one of you lifters is most likely stuck. ATF is HIGH DETERGENT so it will make it unstuck. If you do'nt want to do it this way the you have to take your valve cover off and remove the lifer and replace it for a hefty price. TRY THE ATF firts its cheap and it will help make your car run better too.
Two choices ;
No. 1 - go to parts store and buy a quart of engine flush . Follow instructions on can and change oil and filter . Buy a bottle of Lucas Oil Additive and pour it in . If after driving for a while tapping does not stop , go to No. 2
No. 2 - replace cam and lifters . Never put new lifters on an old cam . Will tear them up in no time .
check your oil, if its a little low it could tap
then check your pickup tube next oil change
if its not low oil or a clogged pickup, replace the lifters that are tapping
with valve covers off, push hard on each lifter to try and find a soft one
replace those ones