I don't know what this noise is if is almost like a ticking noise at idle coming from underneath the cab close to the back of motor

 

Just to be safe, make sure you don't have a plug working loose.

 

had the same noise start up a while ago , as said above my plug popped out . just put it back together last night . check them all and tighten them up before it lets loose , there is a few good posts here about going over your plugs .

 

It's probably your exhaust manifold has a leak like countless other trucks of this generation. Look it up, there's tons of info on it.

 

This^

If its just a mild tick I dont think its anything to worry about. My truck has been ticking for a couple years, you really have to listen for it but its there. Always a good idea to check the plugs though, I had one blow out a few months back, it was not cheap. Still cant believe Ford never recalled the issue.