Thanks for adding this to the common problems list, especially since there has not yet been a common fix for it yet.
I, as with many others here, have had this problem for several years now with no common fix having any effect. The problem is exactly as described here above, happens around 69 to 73 MPH and fades away below or above that ... doesn't come back even way above that

. I can only add with certainty that the speed band at which is starts/stops oscillating will vary depending on whether your driving into or with the wind, so I suspected for a while an aerodynamic issue, maybe a loosened wind dam (which perhaps won't oscilate anymore above 74MPH because it would get pressed back enough in place from air pressure at the higher speeds). Into the wind the ocsilation starts/stops in a lower speed band, and with the wind at your back it starts/stops at a higher speed band.
No one please take this the wrong way, and maybe its because I am so frustrated at not nailing this down by now, but please, please spare us the "It's got to be the: new tires/not getting a roadforce balancing/warped rotors/shocks/swaybar links/endlinks". I, along with may others have "been there done that", and I have replaced everything in the list in the last sentence and nearly everything under the car especially in the rear suspension. No effect whatsoever.
I suspect that those who have claimed that a "vibration" was fixed with certain noted solutions noted above likely fixed some other type of vibration or shake. I still welcome though suggestions from anyone who is positively 100% sure they fixed the exact problem described here: I'm desperate!
replaced everything with the exception of
- the rear trailing lower control arm bushings (can't find an aftermarket manufacturer of them)
- cv axles (as suggested above) but doubt the source of the oscilation is coming from the front.
Someone once noted that generally vibration felt in the steering are typically front-end issues and vibrations in the seats (which is what this sympom is) is typically coming from the back of the car.
Hopefully this thread will be visited by more than one lucky 2000+ owner confirming the same fix for this exact problem. Haven't seen that yet.
I am subscribing to this thread in hopes we will soon finally hear of a fix to this unfortunate problem, most unfortunate for me because it happens at the exact highway speed band I do a ton of driving at.
Cheers!
Mark
The Familyman's Trans-Am
Intense 3.4 MPS, Intense FWI, Intense PCM, copper NGKs TR55's, MSD wires, MSD coils, BWD ICM, MagnaFlow High Flow Cat, drilled 180 'stat, solid front mount, Monroe Max Air rear shocks, Moog rear mounts, Moog suspension bushings, cleared front corners, 190,000 miles
