Sound quality suddenly dropped on iPhone 4s

I've had my iPhone 4s for about half a year now and the sound coming out of the built-in speaker has been working fine until today. I didn't do anything out of the ordinary. I just opened up a video from Youtube and noticed the sound was considerably less clear than usual. When I use earphones, the sound is crystal clear but when it comes out of the speaker, it's very scratchy and fuzzy. Earlier today it was working fine. Rebooting my iPhone didn't help. I don't know if it's a firmware problem as I updated to 5.1.1 as soon as it was availible.

Jus wondering if anyone else has this problem or if there are any solutions out there. Might go to the Apple store this weekend to get it checked out.