4.7s were notorious for spitting rocker arms due to the lifters seizing up. You may have a lifter starting to go bad.

I have taken several apart where the lifter seized & it broke the rocker & the hole in the head when it jammed everything up. A few others it just spit the rocker out & was able to replace the lifters & it was good to go.

No way of telling for sure until the valve covers are pulled & they are checked. I'd eliminate an exhaust leak first though.