I have a 2006 Ford Freestyle and it just recently began a slight tick or knock underneath the motor beside the catalytic converter. It dont tick when its cold and it doesnt get faster upon giving it gas. The oil does need to be changed but im not quite sure that is the issue.

 

If you look, you will probably find the converter(s) heat shield may have broke weld(s). when this occurs, the shield will vibrate against the converter causing a ticking noise. When cold, the shield contracts back against the converter. As the converter heats up, the shield expands away from the converter and starts the vibrate against the converter. Normal fix is either putting a banding kit or the giant hose clamp around it.