1990 Oldsmobile Delta 88 Rattling under hood

There is a loud, rattling noise coming from near/under the engine. The noise is not as loud when I first start the car. When I put it in gear (either reverse or drive) it becomes very loud. When I put on the gas, it goes away. When I turn the wheel ALL the way to one side (like about to do a sharp turn) it goes away completely. After the rattling begins, even if I put it back in park it does not go away. The only time it goes away is when I put the gas on (in any gear, even in park or neutral) or when I turn the wheel ALL the way to one side. I am not sure if this is related, but I just replaced the alternator and the timing belt < 1yr ago. New spark plugs/wires, heater core and radiator. If I could pinpoint a time when it began, I had 3 heavy people in the car when it first snowed. I believe it started a few days after that. What could be causing the rattling? Thank you!