3 second hum every 28 seconds while moving

My boyfriend just bought a '06 Dodge Stratus with only 30,000 miles on it. We noticed a noise today when driving in the country where it is quieter. It’s kind of a hum that lasts about 2-3 seconds and it occurs every 28 seconds on the dot while driving 35 mph – about .3 miles. It seems to come from the right side in the front, but I know that can be misleading. It happens a few seconds sooner when driving faster. It doesn’t happen at all when idling or revving still in the driveway. It doesn’t seem to change anything when it happens (steering, braking, no vibration, hesitation – nothing). It also doesn’t make any difference if we are going up or down hills, foot on the accelerator or coasting, braking or accelerating. Any ideas?

The sound may be from the air conditioning compressor cycling. The next time you hear the sound switch off the air conditioner to see if the noise stops.

Mercedes-Benz had a purge valve (part of the emissions control system) that was located on the left front inner fender well that used to “hum/buzz” in a cyclical fashion. It was a normal operation of the valve activating, but the noise was transmitted through the body and noticeable. Insulating the valve at its mounting to the body of the car helped in lessening the noise. I am unsure if the Stratus was designed during the Daimler/Chrysler merger of “equals” , but if the Stratus utilizes the same or similar emissions system it should be easy to locate the purge valve and check it. Just a thought, and Nevada_545 has also given a good possibility.

Maybe your Dodge Stratus was previously owned by a basketball referee who had something programmed into the car that would buzz for 3 seconds so that he would be prepared to call a 3 second violation while refereeing a ball game. If the problem isn’t what has been suggested above, I wonder if it something about the fuel pump and the noise is being transmitted to the front of the car.