Why does my Blackberry Curve 8330 sound muffled?

When I try to play music on it the music sounds like its being muffled. It doesn't matter what I play it off of youtube,sounds on my phone,etc. It always sounds muffled,but it seems to depend on how low the song is. Like I can play,for example,Demi Lovata Remember December and it sounds perfect. But then I try to play Green Day Know your enemy and it sounds terribly muffled. It does it wit other songs to and they sound just perfect earlier today but when I tried to listen later today it was missed up. No matter what I do it won't change how it sounds. Please help! I miss my music :(