Noisy rattle sound from rear underside of '36 coupe

[Tom B.]

I am getting a noisy metal on metal sound from the rear underside of my 1936 coupe. It happens when I drive on bumpy roads. It's not the spare tire, the luggage rack, the rumble seat, or the exhaust pipe. A friend stood on the rear bumper as I drive and it got a little better. Could it be a shock or a broken leaf? Can fluid be put in the shock?