Did you just rebuild the front end?

If it is an old front end then check all the Bushings.

If it is a recent rebuild check any bushings or ball joints that haven't been replaced first.
Then check the upper control arms to be sure the pivots are tight front and back. If you just rebuilt it you did use the correct cambered bolts when you put the upper control arms in right?

If all else have somebody jack up the car while you watch for movement.