When I start my engine I hear 3 taps then the noise stops... on 1999 Nissan Altima

The car had a constant tapping sound so I replaced the rod and main barrings. The tapping stopped however, when started from a cold startyou hear three taps and then the sound goes away while the engine is running. What is making the 3 taps when cold start?

Asked by for the 1999 Nissan Altima