Loud Popping/Cracking Sound from Speakers

I don't know if this is a hardware issue or not...

The other day, I was watching a video I believe when my speakers started cracking VERY loudly. Singular, loud pops. So I muted it right away, paused the video, and then when I pressed one of the volume keys, I got the popping sound again. It's always the same noise level, no matter how far I turn the volume up, and it's anytime I press a volume button. If I leave the volume on, then videos do not play sound at all, but when I close out of the video, or a Skype beep is supposed to occur because I have a message, I get the same cracking/popping noise. Again, it's the same loud volume level every time it happens.

Restarting makes it stop, but I gave no idea what triggers it to start again. This is the third time. Please help! I haven't spilled anything on it, haven't dropped it...

It's a 15" MBP Fall 2009. I just checked for a software update and I am up to date on everything.

Edit: I plugged in my external speakers and those work just fine. No popping noise from the volume buttons, just the cute little blip noise.

Did you buy Apple care for your MBP? If you have Apple care make an appointment with your local genius bar and have them look at it. Sounds like you may have one or possibly two bad speakers.