You'll always find metal on studs because there are always drywall screws. Move the finder vertically. If it stops beeping and starts again a few inches later, it's screw heads you're finding. If it screams continuously, it's more likely something else. Electrical outlet boxes are generally attached to studs and the wire or conduit may be run vertically along that stud. If you can see an outlet just to either side of where you found the stud and your stud finder gives you a continual metal / electrical signal on that stud then you probably have a wire running down that stud. Pipes might also cause a continuous alarm from the stud finder when moving vertically along the stud, or they may be horizontal and pass through it.