MacBook Pro Stuck on Mute

Hey all,

I've got a mid-2009 15" MacBook Pro and I recently started having the computer become stuck on "mute" where the volume has a white circle with a slash through it just below the volume bar when I try to adjust the volume. Although there IS a chime when I reboot, during normal use there is no sound from the internal speakers, no sound when I plug in headphones, and no red light coming from the headphone jack. I've tried simply restarting, and that didn't work. I've tried trashing the Sound Preferences plist, and that didn't work. I've tried to reset the PRAM and NVRAM, and worked ONCE but hasn't worked since. I've tried, many times, to jiggle headphones (with different sets as well) in the headphone jack and that didn't work. On my last reboot, I reset the SMC. As the computer was loading up, I remembered that the volume setting is available for a very short amount of time (maybe 2 seconds) when the computer first boots up, so I mashed the volume up button and it led to the internal speakers working for the time being.

I doubt that I'll have the same luck next time this occurs, so I was wondering if anyone has any tips that could help me eradicate this problem without going to the Apple Store.

Please, let me know! Thanks!