Motor Noise 2005 GT Mustang?

I have 2005 GT Ford Mustang. Hot or cold there is a clicking noise that coming from the engine. Sounds like "tick....tick...tick..." at idle and the warmer the car gets the louder the noise gets. When I hit the gas the motor the sound goes much quicker, "tick, thick, thick, tick. I don’t feel any difference the cars performance at all. I took it to a service station and they more or less gave me a very expensive oil change. Saying that they added some kind of lubricant engine treat meant that should help. This was over 1,000 miles ago and the noise is the same. Any idea on what this might be?