knocking noise in a 3v motor

a guy at work has a 06 mustang.it has a sparadick knocking noise some where in the motor.one time it sounds like its coming from the front and when it makes the noise next time it sounds like its in the motor.it just comes and goes as it idles.any idea what it could be.its to cold to stand out in the parking lot to try to figure out what it is

Wild shot in the dark but maybe the cam phasers or something with the vct...?

my guess was the cam phasers.my moms 5.4 makes noise and it sounds nothing like her 5.4.it sounds like a rod knock.

Cam phasers are common with those models

Cam phazers, you need to check the cam caps on the right head. If they are scored it's engine time. There is passage with a filter that gets plugged and starves the cam for oil and kills the head.