I really hope your not going through the same thing I did!!! I had a knock sound in my 98 CSVT, took it to my mechanic and he told me it WAS the heat shield and to come back next week and he'd tighten it. 5 days later, driving home from work the knocking got CONSIDERABLY louder and next thing I knew I was broken down on the side of the highway with a busted connector rod and a destroyed engine.
If I were you I would have somebody who knows what they're doing(unlike my mechanic)check it out ASAP.
I still cry myself to sleep at night thinking about my SVT "shell" sitting in my driveway.