IBM PCjr Manual page 239

Part 5 sounds like a motorcycle
gradually gaining speed, remaining at
that speed (pitch) for a second, and
then fading away. After this part of
the Sound Test is complete, a fifth
speaker with a flashing "9"
underneath it appears on the screen.
Press
Did you hear Part 5 of the Sound
Test?
YES - Go to Step 6.
NO - Go to Step 7.
Sound Test 6-97