I recently sent my Beats Studio to Amazon for replacement. The strange thing is that the replacement ones are slightly different to the original ones I got. The bass is definitely weaker. On the originals on certain songs the headphones would shake and the bass could be felt on your neck. This does not happen to nearly the same extent on the new ones. They are also considerably tighter on my head than the originals. Another difference is the absence of a sticker on the inside of the headband with a serial number on it. They're replacements from Amazon so they're genuine.
Is it just a case of a different batch having a slightly different sound or is there something up?