faint noise coming from where you put your oil in

02 trailblazer 4200 motor with 168,000 miles. it is making a slight grinding noise that is coming from the valve cover in the front of the motor where you put oil in. it is only making the noise when it is at an idle. when you rev it up you can't hear it anymore. Any ideas? Is it bad news? thanks in advance

First thing remove belts for a test and see if noise stops.
Post back what that does.