This is the answer I got from the Activision Staff:
Hello, I am sorry to hear about the difficulty you are having with our product.
1)Install the 3rd party "kxproject" Drivers. They Work on all EMU10K model sound card chipsets. They can be downloaded here;
2) Open up "DoomConfig.CFG in your "Doom 3\base\" folder. Scroll down to the entry "seta s_maxSoundsPerShader "0"
and change the "0" to a "1." Save it.
3) If you feel the sound problem is interfering with the games ability to RUN at all. You can go into the SYSTEM
control panel, and then to the HARDWARE TAB, then to DEVICE MANAGER, under "sound video and game controllers" right
click your sound card and click disable. Reboot and then relaunch game to see if the issue is resolved.
4) Again make sure your Bus is not over clocked. Over clocking the bus also over clocks your PCI bus and speed.
Normal PCI speed is 33mhz, if you raise that, it will effect the stability of all PCI cards that are stressed.
If the problem persists, I would like you to generate and send to us a directx diagnostic file. This will greatly aid us in troubleshooting your system. To do this we ask that you do the following.
1) Click on the Start button > Run.
2) In the box type: dxdiag
3) Click the OK button.
4) DirectX Diagnostic Tool will open, click the Save All Information button at the bottom.
5) Save the dxdiag.txt file to your desktop.
6) Login to your account at http://activision.custhelp.com
7) Click My Stuff and then click Questions.
Find your current incident and click on it under the Subject column.
9) Click Update Incident.
10) Under "Attach Additional Documents to Question" you will see a Browse button. Click that and browse your computer for the Dxdiag on your desktop. When you locate the file, double click on it.
11) Once the file appears as attached, you can now enter any additional information about your Incident in the "Results and/or Additional Information" field.
12) Click "Submit Update to Question" to send the Dxdiag