I just bought a 05' F-150 5.4L V8 supercrew lariat edition, it has about 9300 miles on it. When at low RPMs it sounds like there is a small rattle or clicking noise, to me it sounds like maybe it is the engine kicking something on and off, but possibly something bad??? When I listen underneath the hood I can barley hear it but when I stick my head underneath the body it sounds like it is by the exhaust. Any knowledge, suggestions, or help would be appreciated.

Thanks