The Mystery Solved
This from Edwin Outwater, conductor and soon-to-be-blogger, on the Arnold Schoenberg and his Second Viennese School:
I have had this for many years. It's a prank (one of many) played by the conducting staff of the Cleveland Orchestra (including Matthias Bamert, James Judd, Kenneth Jean) during the Maazel era. The narrator is Robert Conrad, longtime Cleveland Orchestra broadcast announcer and co-conspirator, and the raving German thing at the end is the voice of the great Kenneth Jean, an awesome conductor and all-around funny guy.
Mystery solved, for those who don't already know. Now if we can only solve the "who is doing that screaming?" connundrum.