[Sierra5648]

I have a 2006 recon and a loud noise coming from the top end. Runs awesome revs up and drives no issues but there is a horrible sound comming from the top end almost sounds like something is rattling. The motor has been taken apart to tell that the crank bearings are good and top end is as well. Are issues with valve rockers common on these?? Trying to narrow down the possibilities.
Thanks