This was the second time Mario Van Peebles and Ice-T have starred in the same movie. The first time was New Jack City (1991).
Dr. David Corbett:
If You Don't Want To Be On Earth Anymore... Why Don't You Just End It All?
Thomas Payne: Doctor... You Should Know That Suicide Is A Mortal Sin
The chunk which hits San Francisco was reported to be traveling at about 32,000 miles per hour. That's very credible for an orbital collision. However, the firey blob we see impact with the city was clearly traveling at about 500 miles per hour. Something traveling at 32,000 will not be seen before it hits. There certainly won't be any time for someone to hear a rumble (speed of sound is only about 700 miles per hour - anything faster than that you won't hear before it arrives).