The comment about the tach made me remember that I have noticed recently that the cruise control shuts itself off occasionally for no reason. I have also noticed for years that I hear a light whirring noise when decelerating from 25mph or so to zero, such as at a stopsign. It sounds like what I have heard previously to be a speedometer cable problem.
Could any of this be related?
Keep in mind that when I put the gear shift in 3rd, the transmission whine always goes away. Also, the sound is always proportional to load, not rpm.