periodic vibration in car

[goodboat]

What might be the cause of a periodic low-frequency vibration in a car. The vibrations sound a bit like muffled wind-buffeting, on the edge of being unnoticed, and pausing every second or so. The frequency does not change; the vibration just comes and goes. Can be felt, just barely, in the steering wheel, but the sound seems to come from the whole body of the car. Seems more noticeable when car and tires are very cold. Poor tires increase it, new Pirellis lessened it. Have had this '99 Mercedes 4-Matic wagon from 82,000 miles to 126,000 miles. Alignment has been checked repeatedly, 4-wheel alignment (supposedly). This car has full-time AWD but different percentages of power to front and rear, 40 vs 60 percent, I believe. If I take the car to a dealer and ask this question, I'm always told the mechanic can't hear or feel the vibration.

 

[waross]

Have you checked for a combination of an out of parallel brake rotor and a sticky caliper piston?
This will give an interesting mix of symtoms and shakes, depending on the temperature of the rotor and whether or not the piston is stuck, and where it may be stuck. (Or, more accurately, the amount of pressure that the stuck piston is exerting on the pads.)

Bill
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