TH350 transmission noise

[superman3405]

Okay guys I have been installing a new 350 motor on my 72 chevy sb truck now for a while. Finally got it out running this weekend. I have a noise coming from under the truck, I belive coming from the transmission. When I shut the truck off there is a deep rettling noise coming from around the converter area. The Flexplate is tight and in good shape, heck, it is new. I am thinking it may be the convertor. What can I do to troubleshoot this? I am ntoa transmission guy so everything down there confuses me. Thanks!