I also believe there are some sound dampening kits for your hood that may help as well. Does your hood still have the stock noise barrier / dampener material?[/quote]
Still have the stock noise barrier under the hood. good call.
The 7.3's are sure rattely engines, even for a Diesel.
You've probably already looked, but check your doghouse engine cover. Check the seal, as well. Mine came back from being worked on, noticeably louder. I looked at the cover, it looked and seemed fine, until I took it off. They missed one of the tangs. I reinstalled it myself, made a big difference.