Where do you feel this vibration the most? In the steering wheel or in seat of the vehicle?
DOes it happen more when accelerating or when de accelerating?
Ok.. since it does not happen when braking, then that would rule out the brakes... pads and rotors.
However, since it is in the steering wheel, it is definitely in the front end. ANy loose front end part could do this. Loose tie rod, ball joint, shocks/struts or even a bad/bent axle shaft.
In rare cases, loose motor or transmission mounts can cause vibrations as well... but I don't think that is your problem.. but I just wanted to bring that to your attention.
The problem I have is common to the model of car I have. Many others on the net reported darn near replacing the entire suspension system , spending thousands only to drive away with no specific answer to their problem other than they just own a shaky car. I already have an appointment with a front end shop next week and was hoping that you would be able to know a bit more about this particular problem on this particular model. There are a lot of free web sites out there that recommend replacing lower control arms, ball joints, half shafts, tierod ends, wheel bearings, road force balance the tires, etc... I'm dissapointed you didn't recognize the issue letting me know you've seen this before on this particular model of car. Otherwise I might as well be like the rest of the masses and just believe what any mechanic says while forking over my cash. thats why I offered the 30 bucks, experience on this car and model. At least I know not to agree to pay for help on the net anymore.
Well, I am sorry you feel that way.
Here is also a TSB for a vibration/shake on your vehicle from alldata.
Bulletin No.: 00-03-10-007F
Date: February 05, 2004
Subject:Shake/Vibration in Steering Wheel, Floor, Seat at Highway Speeds on Smooth Roads (Diagnose/Balance Tires/Wheels)
Models:1998-2004 Buick Park Avenue, Park Avenue Ultra2000-2004 Buick LeSabre1998-2004 Cadillac Seville (SLS, STS)2000-2004 Cadillac DeVille (DTS only)2001-2003 Oldsmobile Aurora2000-2004 Pontiac Bonneville (17" Tires only)
This bulletin is being revised to add the 2004 model year and delete the screened tire program information for all tire manufacturers except for Continental General. Please discard Corporate Bulletin Number 00-03-10-007E (Section 03 - Suspension).
Some customers may comment on shaking/vibration in the steering wheel, floor or seat while driving at highway speeds (typically between 60-72 mph (96-115 km/h)) on smooth roads.
These specific vehicles may be sensitive to various rotating mass assemblies, especially if they are considered to be out-of-balance.