IPhone 4 Audio/Sound Not Working?

My IPhone 4's audio recently stopped working. The "silent"switch is off, and when I go to the settings and check the ringer sound (scrolling higher and lower), it plays through the speakers as if it is working, but when I get a phone call or text message, it isnt working. My music still plays through the speakers when I use my the IPod on my phone, but the rest of the audio sounds are not working. e.g. the clicking when locking and unlocking your home screen, text message notifications, phone calls. Any ideas on what the problem could be?