I have a new built engine in my car. I can start it and let it idle for 30 minutes but when I get in to drive it I can hear a tapping sound from 2500 rpm to 3500 before engine noise drowns it out. After I drive the car for 10-15 minutes the sound can no longer be heard.

I don't know if this is lifter tap, piston slap or something worse. Some will say bent valves some might say rod knock but the noise goes away after its warm and I would suspect rod/valve noise would get louder or worse with heat.

Thoughts?

 

My 2.3 has been loud since day 1. Im at 9k miles no problems

 

Sounds like piston slap, it goes away when the piston heats up and expands. Your builder gapped the rings loose.

 

Nothing to do with the rings. Piston to cylinder clearance is on the loose side. Make sure you drive it easy until its fully warm and the noise is gone.

 

Mine is as quiet as stock. I used stock sized Pistons. Your motor is built loose I am guessing.