Wasn't there a video for this at some point? I thought I remembered there was.
One possibility... does the transmission happen to have a PTO on it? If it does... is it engaged but not hooked up to anything? When the trans spins, the PTO would spin as well... and the u-joint could be hitting up against the trans body. I know you said it sounded like it was coming from the front of the engine... but its a possibility that hasn't been explored (but happened to me the other day)
