2003 Ford Ranger Ranger

What you hear is the lifters. At times when the engine is off the loose a little pressure and will tap until the pressure goes back up. You can try putting in some marval mystery oil to clean them up so the hold pressure. With only 48,000 miles I don't think they are really gummed up.

There are two lifters for each cylinder, one for the intake valve and one for the exhaust valve, in older cars they had what the call solid lifters. Those were the ones that had to manually adjusted so there was correct clearence when the valve opened and closed. If they were too tight the valve would not close all the way causing a loose of pressure. With hydrolic lifters they fill up with oil and keep the correct pressure to enable the engine to run properly. If they loose some of the pressure they make a tapping sound until the pressure builds back up when the engine runs. In some cases the lifter does not build pressure up and then have to be replaced. They are known as collapsed lifters. See diagram of a lifter