1987 Toyota Cressida Nerve-Splitting Rattle

Hello,
When I am accelerating up a hill or general incline, my Cressida produces a rattling sound that chills my blood
(? Repair $$$). Unless I really gun it, the car can't make it up a hill above 30mph. The rattle doesn't sound much worse than when it first started about a year ago. I have not had any luck getting my mechanic or any mechanic to give me a diagnosis. This deep guttural rattle seems to come straight from the center of the hood, either engine or chasis. This car does leak some oil onto the top of the engine, but has regular oil changes and other routine maintenance.
Thanks in advance for your suggestions.