It's probably a tip issue. When in doubt, I found this useful I'm sure there are more sophisticated ones. I thought the right side was less bassy but, in the end, I'm finding out that one of my ears might be a little different (it doesn't help that many of my tracks have the bass player on the left). Seal is important! Too much insertion can cause less bass with some tips and too little insertion can give the same end effect - it's a constant balance with some tips. Moved up to different tips and I'm all good to go (KZ spiral blue things as L instead of M - great soundstage). Waiting for spinfits/twinblades too. However the small bores might not suit the IT01 sound...will see! JVC spiral dots have big bores but I can't seem to find a reliable source here in France/EU.