I have had a similar issue with my 4 cylinder ranger.
My cam shaft went bad, and there was a very loud very audibal clanging that sounded like you where tapping your keys on the table,
When I replaced the cam, lifters, and all those goodies, I also replaced the injectors. After replacing them I started to hear another ticking like noise. It wasn't as harsh as the cam tick was, it was like some one said earyler, a sewing machine.
Now my buddy's got a 2002 ranger, and his injectors are pretty loud, but with out hearing it it would be hard to tell.