Knocking in the tourque converter or trans

91 s-10 v6 4.3l auto, rebuilt long block, 2400 miles.

I started hearing a knocking sound like a rod was bad but once I took the transmission dust cover and spun the fly wheel by hand and I hear the knocking in either the Torque converter or the transmission, any suggestions how to check them?

Thanks

Please use your other thread.

If the bottom 2 of each side of the transmission bolts are loose and there is a 1/8 to 1/4 inch gap will the transmission or flywheel make a knocking sound. Please do not close this post. The other post is under Blazers, this is a 91 s-10, 4.3 l, v6 new rebuild long block installed.

Thanks