clicking sound

i noticed a clicking sound in my 4.3 vortex engine tonight while ideling in driveway. it is running rough and sounds like a coffee grinder at passenger side floor. ran codes and 43 comes up, knock sensor, but im sure it could be many related things. i think the clicking is egr valve but something has to trigger it. 93 blazer s-10. any ideas out there? i can use all the help i can get. thanks

I had a similar problem with my 99 Blazer, It turned out to be the starter. The gear didn't retract back into the housing and kept being kicked off the flywheel as it rotated