I own an 99 explorer with a 4.0l v6. It was chugging for a while so I took it to a mechanic and they told me my #3 cylinder was misfiring. So I changed the spark plugs and every thing was fine for about four months now it is doing it again. Could it be my distributor? My second question is I have a howling sound that comes from my transmition/drive shaft area. It is not constant but it happens when I apply stress to the engine like going up hill or speeding up to quickly. What is this sound?