thats right. its all down to the way apple have written their EQ software - poorly lol. when you apply eq on a sony or any other decent mp3 player, it might raise the bass and treble by 4db each for example. what it will then do is lower the overall signal level by 4db so that it doesnt cause signal clipping.
Apple though, they dont bother to lower the signal after the eq. so you are left with bass thats 4db above normal and what happens is if the bass on the original recording is near 0db (ie as loud as it can be recorded) then the apple tries to push past that maximum and pushes the signal in to clipping. the result is distortion even at very quiet levels - the signal is clipping even before its amplified.
silly apple.