I think the F-117 may be supersonic - good reason.

Sonic booms are not a result of the plane passing through the speed of sound.
The sonic boom is a continuous waveform that originates from the plane as it is moving through the air at faster than the speed of sound.
As the plane moves though the air, the air gets moved out of the way. If the plane is moving at slower than the speed of sound the pushed air moves aside but moveback in such a way that the air is always in contact with the plane's body. If the plane is moving at faster than the speed of sound the air cannot move back in place behind the plane and a vacuum is formed, as the air rushes in to fill the vacuum it it smacks together producing a sound. All of the leading surfaces of the plane push the air aside, the air pushed aside produces a shock wave of over pressure followed by a area of negative pressure (vacuum). This pressure increase followed by a presure decrease is the typical N signature of a sonic boom, called an N signature because a plot of the pressure vs time resembles a capital N.
As the plane passes a location where an observer is the over pressure followed by the negative presure radiates from the planes location to the observes location. This pressure pulse (the sonic boom) travels from the plane to the observer at the speed of sound so if you are close to the plane you will hear the boom very quickly and it will be very loud. If you are farther from the plane the boom will take longer to get to you and will be quieter (relativley) because the sound dissapates (spread over a larger sphere) as it travels away from the source (the plane)
Thus a plane taking off and flying near the airport rarely if ever cause a sonic boom because it is flying subsonic. The loud noise you hear is just the jet engines which are quite loud.

You sure you are not talking about a F-22? F-117 is subsonic, and was made that way because of it stealth features. It also doesn't have loud engines so you would not hear a roar of them.