Samsung UpStage M620

ok so i've uploaded mp3s on the phone's internal memory and sd card. when i play the songs, it's really low. the volume is all the way up on the main screen/menu settings/and player as well! now, sometimes lets say i change the ringer volume to level 5, then i go to the music player, the first song on the playlist plays at normal volume (pretty loud). but only the first song. ive also tried playing it through the menu/tools/mass storage area with the different player and still the same thing. i'm thinking this is a glitch but i have no idea what i should do bec sprint charges 35.00 for a refurb at store. sucks. any help please?