Engine squeak

Hi, my 350 in my my car has recently developed a squeak that happens as soon as I turn the engine off. I can slightly hear it at idle but it is very faint and will go away if I give it a little gas. Ia m not sure if it is one of the pulleys or something in the engine. The sound is coming from the driver side and it sounds like it is coming from under the valve cover. I pulled the valve covers and started the engine and did not hear it coming from the rockers. Although I still heard it on the same side. Not sure if it is something mechanical but it is the loudest when I shut the engine off which is what made it more noticeable.

Thanks