Hi Larry:

First, may I suggest that you repost this in the "Engine & Exhaust" forum? You'll have a better chance of getting a satisfactory answer -- more people will see your post.

That said, I also have a 2004 coupe that one day, after about 25k miles (iirc) developed valve chatter that was quite prominent, varied with RPM, etc. I had to take it in to a local dealer, and sure enough, about a week later I had new lifters. Here's the thread.

I use only Shell premium gas. OTOH, I was not the original owner, so who knows what was put in the tank for the first 14k miles or so.

Anyway, runs like a champ now. So a happy ending.