I'll start off saying, I hate these kind of threads and here I am starting one. It's very hard to describe what's going on without being there in person but I'll do the best that I can. Driving my '62 Polara, 440ci. with the original pushbutton transmission (rebuilt), I'm noticing a harmonic type of sound that's more pronounced in the transmission's location. It's not coming from the rear of the car but in the hump area in the floor. It puts me in mind to the harmonics that you would get from a fan or a worn bearing or maybe a worn gear. It has a steady cadence like a whirl, whirl, whirl. It is about the same level as the header, dual exhaust note and you really have to pay attention in order to pick up on it. This takes place at 1800 to 2000 rpm, running between 45 to 50 mph on a level, cruzing road. As this is taking place, I can put it in neutral and it immediately stops. Place it back in drive and it's back. I have heard that torque converters can do this but there's no other signs of shifting problems or delays placing it in gear, noises ect. The trans was a high milage unit and was rebuilt by a very reputable shop. The only real problem that was found during the rebuild was a worn tailshaft bushing that was replaced. Let the past experiences with this condition commence!