Thanks for the replies!
I don't know if this is just a coincidence or not, but I put a tank of Shell V-Power in and the noise isn't near as bad. But it is still there. (I filled up before the reply was posted.

) I don't have that great of an understanding of car engines, but if the valves have oil in them, then the gas shouldn't have anything to do with it anyway.....?
I'll try the synthetic oil. As far as the weight, I do use whatever the book says, can't think what it is off the top of my head. I've never used anything thicker. A friend also told me of that recently, heavy oil can cause problems in the cold.
My boyfriend still thinks I'm crazy

for worrying about it. He says it's no big deal. But I'm going to try the synthetic anyway. I don't like my car to make noises that it didn't used to make.
Thanks again for the suggestions!