I had the same issue for a while but in the past week it sounds more like an engine knock. I have seen the check engine light come on in other cars and usually changing the plugs made it disappear. My car does not have the check engine light but the knock really starts above 2000 rpms and is pronounced now. What used to sound like the problem described in this post has become aweful sounding and I am tentitively taking it in to be fixed.