This is going to sound silly, but put on the headphones without a cable attached and tell us if you hear the hiss. My idea is that you may have some Tinnitus or the pressure from the X2 for some reason is causing a problem with your ears.
What are you plugging them into? It could be a bad source, bad music, or some other issue. Please list your audio chain such as:
PC --> USB --> m903 DAC --> BUDA amp --> noontec Zoro HD II headphones