Distorted/muffled speaker sound
For clarification, this is the bottom speaker, not the earpiece.
iPhone 4, iOS 4
iPhone 4, iOS 4
I was having the same problem, I know this sounds silly but make sure that your headphones are completely plugged in. Mine appeared to be fully in, however when looking closer I saw that the case was blocking it a little bit. Once I pushed the plug in as far as it could go, the distortion was gone. Hope this helps!
Distorted/muffled speaker sound