Noisey Lifter

Marvel mystery oil works great for just this kind of thing.
If a lifter has a build up of any kind it cannot work smoothly and is always worse with a cold engine.
All lifters bleed off oil but sometimes the plunger will stick and not pump up right away causing a loose push rod and rocker condition.
If it goes away when the engine heats up then you will be fine.
Put a hole quart of Marvel in the oil and change it to a lighter 10w30.
good luck.............:thumbrig: