One problem related to engine clicking and tapping noises has been reported for the 1999 Ford Mustang. The most recently reported issues are listed below.
1) a ticking noise began coming from the upper middle of the engine. After a month, 2) the ticking became a 'tapping' that became increasingly louder. Enroute to have it examined by a local performance shop, there was a loud sound similar to a gun shot and an instant loss in power. This occurred at 2000 rpm. Upon examination, the spark plug had been ejected from the 2nd from the last cylinder on the pass. Side bank. Such force was exhibited that the mounting tab of the ignition coil was broken and the coil was shattered. Upon examination of the head itself, the plug threads were completely stripped. 3)true blue performance, a Mustang specialty shop, examined the parts and concluded that the only remedy viable was to replace the head, plug, and coil.