and yes, I've tried multiple sources
f*** you, Audio Technica. thanks for nothing
I don't know why you went with the M50 if you want a bassy headphone for hiphop. My guess is you probably got some bad advice from some audiophile who don't listen to bassy music and/or hiphop.
If hiphop is all you listen to than grab yourself a V-Moda Crossfade LP2.
Mine sounded nothing like that. On some songs which emphasize bass however there was that "rattling". It's an audio signal though. Best way I can describe it is by listening to the intro to Slam by Pendulum. At first I thought something was wrong but they were intentionally going for that subwoofer feel