What would make a popping sound under the hood of 1999 contour?

A popping sound under the hood of a 1999 Ford Contour could be caused by several issues, including a faulty spark plug or ignition coil, which can lead to misfiring. Additionally, a vacuum leak or a problem with the exhaust system, such as a damaged muffler or exhaust leak, could also create popping noises. It's advisable to have the vehicle inspected by a mechanic to accurately diagnose and resolve the issue.