What year, engine, and anything else is your Ranger. Mine has just started similar noises and it just hit 68,000 miles. I have been told that if its coming out of the valve covers then its a loose rocker that needs to be tightened and if its coming from the center of the engine then its lifters. Not sure what to think though.
2003 Ford Ranger Edge 3.0L Vulcan Auto Tranny
MAC Performance Ram Air Intake
Flowmaster Super 44 w/ tailpipe before the wheel
Interior and Exterior LED w/ music interface
Ford Racing front and rear Sway Bars
Limited Slip with 4.10 gears