Originally Posted by dropnosky

did you move your fan shroud when you put the cooler lines in? maybe the shroud is not seated properly, and the fan is kissing it, maybe even just slightly under load when the engine twists a little.

I agree that sitting in park on two wheels should not have damaged it, I guess theoretically you could have bent the parking pawl, but I doubt it. Heres a pic of a parking pawl that shows how unlikely that is-

I found this on the internet, so its not a MB, but shows generally the setup of a parking pawl pretty clearly-