Engine run in question

[cudamadd]

Hi so we started the 340 to day full rebuild engine run the cam for 25 mins at 2000rpm /2500 rpm not sure exactly. Great temp no leaks all good oil pressure 70 psi 80 and so on . My question is when engine is at 3000 rpm there is a light rattle .we think it sounds like the rocker arms .The break in oil we used was 15/40 Penrith.NO NOISE at idle very smooth and responsive. Basically x heads stock manifolds
After it passes 3000 rpm noise goes away. Its a 69 year 340 . I know on non compression stroke the rockers are a little loose rocker tips are dead centre over the values and so on . Is it normal for a little rattle ? I am thinking that thicker oil will help ,thanks for your time 

[Rich G.]

Shouldn't have any noise and heavier oil isn't going to help being you have good oil pressure. I'd check to see if all the rockers are getting oil up there. Is the timing advanced to far and it's a ping your hearing? Just a thought.

[cudamadd]

No ping noise time at 32/34 dec thanks for your reply

[Chryco Psycho]

If the rockers are used & you put in a higher lift cam there can be ridges on the rocker where it rides on the valve tip this can make noise as it rides over & off the lip .