As per the feedback I recieved, I climbed under my rodeo and tried to bang on the heatshields, exhaust and just about everything I could see, and did not find anything obviously loose or rattling around. My exhaust seems to be rock solid.

Here is another thought though. This whine always occurs at the shift point which is around 2000 rpm plus or minus 100 rpm, regardless of what gear I am in. Once it moves below or above this shift point, the whine ceases. I would think that if it were something loose, It shouldn't be only at this one point regardless of whether I'm in 1st, 2nd or 3rd gear.

If this is something internal, does the fact that it occurs in 'driving' gears as well as PARK and NEUTRAL rule out the torque convertor, or implicates the torque convertor? Can I rule anything out based on this observation?