High pitched squeel/squuek from under rocker cover?

[max69vk]

I have noticed that when I turn off the engine there is a high pitched noise that seems to be coming from under the rocker cover right where injector 4 is located almost like a high pressure squeel. Below is a short vid of the high pitched noise after shutdown, despite it coming from the injector area under the rocker cover & the master-tech not even getting anywhere near the engine bay or even explaining what else it could be, I've been told its nothing to do with the injector...

6cc4b365.mp4 video by max69vk - Photobucket

Anyone want to take a guess what it could be as I'm clueless?!