ATH M50 - A small problem in left-right balance. Please help?

Hello Everyone! 

I bought an Audio Technica ATH M50 headphone 3 days back and I'm loving it so far but there's this small problem that's bugging me. 

I mostly listen to electronic music and I love the bass-rumble feeling. However, I noticed that in some of the tracks, the left ear cup rumbles more than the right earcup. Not significantly but one can tell the difference easily. If i adjust the balance to 25% right everything's fine but I can't help thinking there might be some problem with my headphones :/

Is it just me? Or you guys too have faced a similar "problem"?

Done! This time my right ear experiences more rumble than the left year so yeah it's not really a problem with my ears i guess. 

I actually set the balance to 100% right and 100% left and it seems the bass is slightly more in the left earcup(the one in which the wire is connected) then the right earcup. :(

Bump. Can anyone help me out? Do you think it might be because of my onboard laptop sound card (IDT HD) I've bought them from the authorised dealer of my country so I don't think these are fake. 

@Amorgan - Yup! Tried that. Problem persists :(

@bcasey25raptor - Every headphone? Really? I'm can't get myself to believe that :| I actually tried playing 7 different bass-heavy songs and this left-right balance problem happened in all the cases. 

PS : I've turned the equalizer on with the 70 & 180 Hz frequencies set at 7.5 dB. I'm using Winamp.