; enter the machine language monitor

  CALL -151

; toggle the speaker and load the accumulator with the "floating bus" value--the byte last read by the video refresh controlled by the video scanner.

  0300-   AD 30 C0   LDA $C030

; print the accumulator as a character

  0303-   20 ED FD   JSR $FDED

; repeat (loop by going to 0x300)

  0306-   4C 00 03   JMP $0300

; run it! (0x300 Go; just like G in your debugger)

  300G

Running this will display random characters and make noise.