Could be a bang or poping noise. The idle and/or performance should be altered as well if a pair of plug witres were reversed, as two cylinders would not be providing any power.
To check, google "firing order for a Ford <enter your year and engine size here>"
This should net you a site that has a picture of the engine, marking its plugs and firing order. Pre 2005's have one coil pack, correct? Not sepereate coils (CAP) per cylinder? If each cylinder has its own CAP, then one of those may be bad, and you should have a code (CEL) stored for it.
It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt.