Transmission noise

[63chevy4x4]

Maybe this is the wrong place to ask but here goes. I put a th350 in my 61 gmc and it all works fine except when i have it in park with the brakes on there is a strange sound, like a metal to metal rubbing sound sorta like the sound when you break a rusty bolt loose, it happens everyonce and awhile and sometime right when i relese the brake and start to move. It dosent do it in reverse just forward, any ideas??