700r4 noises or 383 stroker piston slap?

[stringpickin]

Hey and good day.. Thank you for your time and help.. I recently put a new engine in my truck and did a 700r4 conversion.. I have a noise that has developed in my motor that seems is going to make me have to pull it out and have it torn down.
But, I remember that before or just when the noise started I took my truck back to the shop where they put the Transmission in and had them rotate the flexplate 180 to see if we could get it to balance out bit more. I didn't think about this until today and now I am wondering.
I went and picked up my truck and started it up and heard this noise that sounded much like a rod noise to me and or a very loud clapping type noise that I had thought I had heard developing slighly before dropping the truck off at the transmission shop.
Research has lead me to believe that it may be piston slap. It is 383 built by Smeding performance, a highly recomended builder by Edelbrock and a brand new engine from the block up.
I have pulled a wire at a time and the noise never disapeared. The noise seems to be coming from the back of the motor. As soon as the motor gets up to running temp the noise is all but impossible to hear.
My question is about the Trans. Is there something in the Torque converter and or flex plate set up that could be causing this type of noise? Any and all experiences with engine noise or 700r4 noise is greatly appreciated.
I hate to pull the motor if it is a trans problem. What came to me today while thinking about pulling the motor was remembering that the noise was seeming to just start occuring at about 350 miles on the new engine and trans.
and I remembered when I picked up the the truck after they had turned the flex plate that the noise was terribly loud. But went mostly away after warming up.
The truck hadn't sat any longer than it had in the previoius days/weeks before I picked it up at the trans shop. Tempuratures about the same, mid 40's.. So I am wondering because of that time I picked it up and noticed it being so very loud, could it be transmission related. And of course any engine related noise advice very much appreciated.

Thank you thank you for any help..