Normal. Vehicle leveling syatem.
I just purchased a 98 STS and have heard that same noise.. Happens when the key is first turned on, but continues once car is started. I tracked it down, atleast my noise. Next to the headlight switch there is a really small vent, I am guessing it is for climate control. I put my hand right in front of it and can feel air being sucked in. It sounds like the bearing is shot in mine, it gets quiet after a min or so but can still hear it.
It it is a very slight shake this may be normal. Engines make vibrations and vehicle design engineers are less likely to waste time and money hiding this vibration on a truck than a car. Generally, trucks are meant to be practical more than luxurious. If it is a severe vibration, your engine may be running poorly or you may have a vibration transfer problem.
Rotors may not be balanced, calpiers may be installed incorrectly, tires may be out of balance or mounted wrong, wheels may be bent, steering linkage may be worn out or loose.
If you have average mileage on it, you should go get it checked. That is too low for an idle. The vibration is probly from the low idle.
check front axle bearings.
tension on the motor causes a slight vibration in the on the frame of the vehicle
Perhaps because of the earthquake slight vibration let balance change, by qpstore answered
She made a slight adjustment to her dress before leaving the house.
Probably need to rebuild the transmission.
A rebuilt transmission shoud perform exactly like a new one. Hesitation is not normal. Take it back to whoever rebuilt it.
Quakes move nearer to the surface as an eruption approaches. And these "microearthquakes" happen more frequently before an eruption, until all the seismometer can register is a distinctive vibration, slight but continuous, known as a harmonic tremor. The seismic activity associated with volcanism is usually as a result of pressure increases in the magma chamber....
The driveshaft might be out of balance or dented in some way, also check the u joints
Consider the possibility of a bad differential or wheel bearing. Is it a grindey scrapey noise? If so suspect wheel bearing or differential. If car is lifted off the ground and trans in neutral, frmly grasp each tire one at a time and rotate. If a slight vibration is felt, replace that bearing. This vibration is very slight so pay attention, okay? If not show any vibration, expect a differential (or possibly but not likely transmission) problem.