Even then an air leak does not a loose rib make...plenty of good ribs have small voids in the solder that would leak air....Id bet its solder balls that were not moving b4 all that boiling or the base of the old front site if the rib is tapped all the way through.....fill the void in the rib [through the weep hole] with a heavy oil letting it flow all the way to the muzzel....then let it drain back out through the same hole.....this should stop the rattle for the forseable future and also help prevent any rust that might form under the rib...
