I have an automatic. When it is in park or netural, there is a loud thump from the transmission hump, I touch the brake, or shift into reverse or drive and it is fine.
sound to me that your CV joints are bad or broken . it could be your stabilizer to your tranny also there is two round bar that go to the side of the block to the top or middle of your tranny . and if thats not it try putting a jck under the tranny and juck up tight to it and then just see if your trannt moves if so u might have tranny mounts trhat need fixed