olds 307 knocking?

I am just trying to gather some thoughts here. I have an 0lds 307 in my 1987 442 that was re built two years ago. It has less than 5,000 miles on it. It started knocking on me, sounded like a lower end knock. I pulled the torque converter back, inspected the flex plate, and started it, it was still there. I did a little more visual inspection, listened around, and pulled valve covers just for kicks. I then pulled the engine and took it to who built it. they tore it down and checked everything out. There was nothing wrong with it. I then talked to a co-worker of mine and he was thinking it was an exhaust manifold leak. I too think it might have been that, I just never heard a manifold knock like that. It was a knock not a tick. Here is a bit of info about my manifolds. When I first put the engine in I had the wrong manifold gaskets, leaked like crazy. I then removed the manifold gaskets and put orange hi temp rtv on them and stuck them back on. Both of my manifolds are cast. After removing the engine there was no obvious signs on the heads of a leak, but the manifolds looked a little dark in some areas especially the manifold on the side where the noise was.
Just wanted to pick your brains a bit to see what you all thought. I'm waiting on some gaskets to get here and the RIGHT manifold gaskets this time to get here. Then I'm am putting it back in and seeing what happens.

I do have air injection tubes. New lines. New valves. New pump. But i will check it when i get it back together and running.

We determined it wasnt a rod knock the motor was tore down and had no problems. The noise never went away it was always there. Mainly at lower rpms it seemed like

I didnt remove any belts. It was clearly coming from the back right so i though..... but thats another place ill check if its still there.

plmberkevin said:

Check the all the bores and all the pistons may have a hurt skirt and it will cause a rattel.

Click to expand...

That was checked.