Sound leakage in Monolith M565C

[candideb2]

Hi, so I got a new M565C from Amazon. My friend was sitting next to me and told me he could hear the music I am listening to. Does this mean I got faulty headphones? They are closed-back so this means that they should not leak sound. Should I return them? Do all M565C suffer from this? I could actually get the M1060C if I return the M565C but I don't want to mod the 1060C as I am a newbie, and I am also intending on getting the M1070 in the future. I hope someone would give me an advice.