Steve's original post inspired me to look up a perennial favourite of mine - the wonderful Portsmouth Sinfonia.
Here's what Wikipedia has to say:
Bryars was interested more in experimenting with the nature of music than forming a traditional orchestra. Instead of picking the most competent musicians he could find, he encouraged anyone to join, regardless of talent, ability and experience. The only rules were that everyone had to come for rehearsals and that people should try their best to get it right and not intentionally try to play badly.
And here they are playing Riachard Strauss's Also Sprach Zarathustra
. I love the completely random toots.