Unexplained peak cluster in proton NMR trace?
You are correct. The chemical shift of methyl protons 1 and 4 are close to one another.  You still see the two expected triplets, they just have similar chemical shifts.  That's not too surprising since they are both methyl groups attached to a methylene group.  We could tell which triplet belongs to which methyl carbon by measuring and comparing the 2 sets of CH2-CH3 coupling constants.