New engine new problems

I had a motor like that, it would be silent until the RPM's went over 10,000 then you could hear the pistons smacking the head as the rods stretched I imagine. I turned out after taking it apart the machine shop decked the head at an angle and took too much off and of course I didn't check before assembly, I just "assumed" he knew what he was doing! So, ruined the head, pistons, and rods in a few seconds...The worst part was they refused to make it right because I didn't check before assembly. grrrrrrrr

Decking the head won't cause the pistons to hit the head, it can allow the pistons to contact the valves if the seats aren't cut to lower the valves to the correct depth.
Any time the block is decked piston protrusion must be checked to see if a oversized head gasket is needed.
With a decked block, milled head and higher lift cam you could have pistons and valve kissing each other.

My block had been decked .010, pistons protruded .008-.012 above spec requiring a .010 over head gasket. Valves where at min spec depth and I had installed a Colt stage 3 cam bringing valve to piston clearance closer than recommended.
To prevent possible issues I installed a .020 over head gasket, 12k miles of heavy towing with no mechanical issues so far.

For S&G's loosen the valve adjustments another .010 on every valve. You'll have a noisy valve train but if the other noise goes away you'll know what the problem is.

You're right I should have said the block, I didn't check, just put it all togeather. This was a very long time ago, but the pain still lingers!

I think I'm gonna try a bore scope. It's not just paranoia, hell I just finished up a mostly stock rebuild to today and fired it up on the stand. I need to check pushrods and buy a small bore scope I guess

So a little update

Borescooe didn't work great and after talking to machinist, I decided to pull the head. He feels like it's a valve sealing problem. Well just got the head of 5 mins ago and it appears no PTV problems. So the head is off to him for some inspection while I'm out of town for work the next 3 or so weeks. Hopefully he finds something wrong with a seat or something and can fix it by the time I'm back.