Self-mode-locked　noise-like　pulses　(NLPs)　were　experimentally　investigated　from　a　normal　dispersion　erbium-doped　fiber　laser.　Different　from　noise-like　pulses　with　a　broadband　spectrum,　the　self-mode-locked　NLPs　have　a　narrow　optical　spectrum　of　1-2　nm　and　hundreds　of　nanoseconds　duration.　However,　the　intra-cavity　maximum　energy　of　NLPs　is　up　to　560　nJ　without　pulse　breaking.　The　higher　pulse　energy　output　is　promising　in　the　proposed　fiber　laser.　To　confirm　whether　self-mode-locked　NLPs　are　caused　by　an　invisible　nonlinear　polarization　rotation　(NPR)　mechanism　owing　to　slight　residual　polarization　asymmetry　of　the　fiber　and　components　used,　we　compared　the　output　characteristics　between　self-mode-locked　NLPs　and　NPR　mode-locked　pulses　in　the　same　cavity.　The　experimental　results　show　that　the　formation　mechanism　of　such　self-mode-locked　NLPs　could　be　related　to　a　weak　NPR　effect.