Why does my laptop speakers keep turning off and on?

I have a HP Windows 7 had it for almost a year now. Well of late my speakers don't work like they are suppose too. The sound quality is the same and all that. They turn on and off. Most of the time they are off even though I am playing music with the volume full blast. It only works when I pull out the earphones or mute and then unmute. When it works again it only does so for about 5 seconds and then I can hear a crackle/ popping noise and then it turns off again. If I repeat either the two methods my speakers will work again but only for 5 seconds like I said. What the hell is wrong with it?