Do you notice your RPM's moving up or down during this noise? If at all possible take a video from inside your car so we can hear the sound it's making. You said your having a rough idle. The first thing that I would check would be a loose vacuum hose somewhere. Second, how many miles are on the car? It could use some new plugs and wires. The car is most likely having a misfire somewhere and I would suspect a tune up is in order if your above 60,000 miles.