May be a lifter that is deflating. I would change oil and use 5w40 with lots of detergent additives and see if the lifter will clean itself. If the tapping continues, it may cause cam lobe damage. Is yours a 454? Old school chev v8s had a cam lubing problem with the rear two cylinders, not so much in the big blocks but common in the small blocks (350, 327, 305 ect).
Dave and Laura & two cats
02 Discovery with Accord toad
retired auto rv tech and teacher, wife rt nurse