Mono audio after startup

I'm using OSX 10.6. After startup the audio is set to mono in the Universal Access in System Preferences. I perfer stereo audio and have to uncheck the "play stereo audio as mono" box. I would rather not have to go in and switch this every time I boot up. How can I get this to default to stereo audio after startup?

Have you checked your startup items? See if anything there is causing it to happen, maybe try resetting the PRAM reset, Shut down your Mac.
Locate the following keys on the keyboard: Command (⌘), Option, P, and R. You will need to hold these keys down simultaneously in step 4.
Turn on the computer.
Press and hold the Command-Option-P-R keys before the gray screen appears.
Hold the keys down until the computer restarts and you hear the startup sound for the second time.
Release the keys.

I tried resetting the PRAM and disabling all startup items to no avail. Anything else I can try?

I personally do not know of anything else that I would try, maybe someone else can help you with it, sorry I couldn't help. Have you tried reinstalling OS X?

Thanks for your help - I'll try reinstalling the OS

In case anyone else runs into this:

Reinstalling the OS didn't work but I (accidentally) fixed this problem by deselecting mono sound in Universal Access preferences, selecting a different sound output device in sound preferences, rebooting and then switching back to the built in audio output. Now boots to stereo audio. Don't ask my why this worked, just know that it did.