How can i reduce my roosters crowing?

our rooster is more than 4 years old with his sister..my son adopted them from school..we love our chooks ..but he has been driving us and others crazy from excess crowing ..he crows at everything,phone ringing,looking at him,any noise,floor board creaking,talking,you name it ..he must crow over 200 times a day somtimes more....if no one is home and nothing makes a sound then he is quite for hours...he seems to know when our car pulls up and then starts his crowing...if we carnt find a solition then we will have to take him to the vet to put him to sleep....and no one wants him because 1 hes a rooster and 2 he constantly want to fight you everytime you go near him..we just walk around the backyard with a rake or broom..as we have for past 4 years.........any advice people !!