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?