Mine were defective.
I've sent them to Philips and they told me they don't have any pair to replace them with (product out retired from marked).
They are proposing replacing them with a similar product having the price I've payed to Massdrop (99€). I'm sure Philips headphones in with that price won't be as good as these ones.
I'm now waiting for Massdrop to write me back, if they are able to replace the defective unit or not.