What is wrong with the sound?

My iPod's sound is always messing up. I will turn it on, and it will sound kind of crackly. And if I turn it up loud, I can hear the music but it sounds like I'm listening to a radio station with a bad connection. It hasn't gotten wet, I haven't dropped it, nothing happened to it that I know of. I know it's not the headphones because it's the same when I put it on speaker. Sometimes it does this and then sometimes it goes back to normal. But it hasn't been normal for a few days now so I am getting kind of frustrated. What the heck is going on with this thing?

Thanks so much. :]