1998 Mercury Mystique LS
2.5L V6 Duratec Engine
Automatic Transmission
Approximately 142,000 Miles

The problem first started roughly 6 months back but only at start up and lasted for 2 seconds max. Now that the warmer weather is upon us it has gradually turned into a constant loud clatter. This can be heard from in the house if the car is in the driveway (if your listening for it of course). It pretty much makes the car sound like a sick diesel. The noise seems to be isolated to the passenger rear side of the motor. This is my girlfriends car and I have never worked on a Ford manufactured vehicle a day in my life. I would associate this with a severe lifter tick but as I said I am used to Chevy's. Is there anything I might be missing that would shed some more light on this issue? If the timing of the vehicle was off would the spark knock become that loud? If it is the lifters is that quite a tedious job and could I use a good oil stabilizer to quite it down? Anything you guys can throw at me I sure would appreciate.

Rick