Deere 648H fuel rail pressure issue

I have a 2014 deere 648H with 6.8 liter engine. It has a flutter with a fuel knock noise at any given rpm when you hold throttle steady. No smoke when it does this. Fuel rail pressure will drop 2-3k psi at 1600 rpm when it does this. No codes. Any ideas? I will try to post a video of it. I replaced fuel filters