Please speculate on what could be causing my noise/vibration
It's a 1996 Thunderbird 4.6L and 4R70W. Here's the symptoms:
At low city speeds, like 60 km/h, at very light throttle, there's a faint whirry/humming sound. I can almost make it happen on and off at will by pressing the throttle very lightly and releasing it.
Also, during certain city speeds and upshifts, or if I feather the throttle like I described above, I can often produce subtle but noticeable "bonk" or "dunk" sounds.
Third, on the highway, at 100km/h and above, the whole car vibrates noticeably. I can feel it everywhere, steering wheel, floor, even my face. Seriously, it's ridiculous.
This has been going on for years. I think I've eliminated three possible causes.
I went from my stock driveshaft to a Dynotech from Evanoff to another stock driveshaft from another car. Problem still there. I also swapped on a friend's wheels and tires and went for a test drive. Problem still there. Last winter I had a new engine built and installed. Problem still there.
I also once jacked up the rear of the car and spun up the drivetrain with the rear wheels spinning. Noise and vibration were there with this setup too.
About ten years ago I had some upgrades done to the transmission like outlined in Jerry W's paper, and I had an Auburn Pro differential installed. Car ran fine for years after that. Anyone got any ideas?