[Christ]

When you put your car into park, you've essentially put it into another Neutral, except with a tab that engages a part of the transmission to prevent it from spinning.

That crunching noise that you heard was just that tab trying to engage the transmission. If it catches, it will either lock up your tires, stop you instantly, or break something in the transmission, all depending on outside affecting conditions.

This is why you set your parking brake on hills in an auto. It's not to keep your car from rolling (nice thought, but no.) it's to keep your car from fully engaging the park tab, making it difficult for you to get it back out of park... (yeah, you've had those times.)