iPhone microphone problems - low volume, muffled

Hi guys,

I am having problems with the microphone (bottom of phone next to speaker) on my iPhone 4. During phone calls people say I sound like im in a tunnel, my voice is very muffled and quiet.

I've tried making a voice message to test if it is something specificly related to calls but when I playback the message the volume is very low. This has brought me to the conclusion that its a problem with the mic not with the software or applications.

Has anyone experienced similar problems? Is it possible to fix this?

I hope someone can help.

ps, phone is outside of warranty or Applecare.