Quoted from bkxdream:

Check Function 39 in the settings. 01 = background sounds, 00 = no background sounds

Quoted from slochar:

That's not right at all. Time to test the sound board inputs, one is probably missing due to either cracked header, or a bad 4069.
The PIA on the MPU board could be bad as well.
Or the sound rom is wrong although I doubt that.

Quoted from pincoder:

Some of the sounds in williams games are cyclic. That is, the sound card is told once to play a sound and then the sound card plays it over and over until its told not to. When the sound increases in speed/intensity like that its because the the sound card has been told once again to play the same sound.
What im saying here is that there is a communication problem between the MPU board and the sound card.
It could also be a problem entirely on the sound card. Disconnect 10J3 on the sound card or 1J8 on the MPU board and turn on the game. if the sound problem goes away the problem is NOT on the sound card.
You can also try these test ROMs: http://pincoder.ca They will help you track down problems with your entire machine. The sound test ROM will be the most use to you.

Quoted from pincoder:

OK good.. the wires on 10J3 are used to instruct the sound card to play a sound. With no signals getting to the card it does like it should and not play ANY sounds. The fact that when connected you have sound playing, albeit the WRONG sounds at the wrong time means the signals to the card are jumbled.
Each of those wires represent a binary digit (ground or no ground). To get the sound card to play a sound, the MPU board grounds a specific combination of those wires momentarily and then un-grounds them.
If you download the pincoder ROMS and look at the instructions for the sound test you'll have a better picture of how it works. Basically, I think one or more of those wires to the sound card are either stuck on ground, or are not grounding at all. This is what produces the incorrect sounds.
So, you just need to test each of those wires to see if they operate correctly. The pincoder sound ROM will help you troubleshoot that.
If you dont have a chip and programmer, you can start by testing each of those wires to see if they're stuck on ground. Turn the game on and go into audit mode (so you know that no sounds are supposed to be playing) and then check for ground on each of the wires. None of them should be grounded. That will at least give you half of the picture.
To reliably test the other half (whether they go to ground when they're supposed to) you will need to run the pincoder sound ROM. It is possible that you could also do this running the built-in solenoid diagnostic (you can on system 3-6a). I'm just not sure the solenoid test on a system 7 can activate sounds or not.. (I no longer have my black knight).

Quoted from PINTEC:

Corrupt PIA check all sounds signals controlled by IC 36
Cpu connector IJ8 sound signal output.
There are two additional signal wires on plug Ij8 from PIA 36 (Solid Purple & Brown with white dashes) that control all commas on the displays.[quoted image]