Without hearing the noise I would ask if the furnace makes the noise when the burners are not on. It depends on what you are decribing as starting and stopping. Where is the noise heard? is the noise comming from the burner compartment-near the blower motor or at the return air grill. A lot of times when the ductwork is sized improperly the return air grill will vibrate from the volume of air traveling across the face of the grill. A blower motor can also make this type of noise if the bearings are going out. Try to iscolate the problem by putting the thermostat selector switch from the auto position to on this of course is the fan selector switch. Keep in mind that the motor will not turn off again until you put it into auto again. If the noise is not aparent with just the fan motor running then try the unit in the heat cycle and then in the cool cycle. Determine where and when the noise is comming. The service guy may have over looked something.