Lifter noise

I own a 2000 Blazer LT it is 5 yrs old but in mint condition. It has 39,750 miles and last night on start up tapping noise in engine. Went away after 4 or 5 min. Keeps recurring on start up. Had oil changed and still has lifter noise. Took it to auto mechanic which he verified was lifter noise. At 39,000 miles. Regular maintence followed religiously since purchased new. Any ideas or recalls? I can't find any tsb or recalls on this particular problem. Thx.