I have a 1998 Explorer With a SOHC 4.0 engine and it has been making a weird noise as if something was lose and rattleing around when my truck hits 3000 rpm. So i was wondering if this has happened to anyone else?

maybe one of your pulley bearings is going bad. What kind of rattleing do you hear? does it speed up as your engine does. check the bolts that hold the pulleys in place. I changed my idler and tensioner pulley on my 2002 explorer.hope I offered some kind of help.

Check your PCV valve and hoses. I had a pcv plug up causing the oil to be blown out of the rear main engine bearing and seal, in return making a funny bearing sound. It stumped mechanics for months, by the time it was figured out the damage was done. VERY expensive if not corrected. Good Luck.