i got my brand new m8 a week from today, everything perfect, checked the phone for any imperfections when i unboxed it and i seemed well.
the next day i went out, kept it in my pocket and took out the free silicon case that it came with and noticed this strange MYSTERIOUS loose volume rocker that everyone is dealing with.
googled the issue and found this thread, and after thinking this is not such a big deal i decided to ignored it.
yesterday i noticed it's not as loose as was before and i took a closer look at the thin frame around the volume button and i have to mention that mine was rock solid when i took the phone out of the box.
the thin frame around the volume button was just a little, barely noticeable, curved and this, suddenly explained everything.
the m8 is quite a big phone, very tall, almost hanging out of the pocket. I also ride a motorbike and when i have it in my pocket i feel it kinda squeezed. Some of you said this issue is a quality check fail of the manufacturer but this phone being made out of aluminium which is easily maleable, has it's flaws.
I just used a thin cleaning cloth to cover it and not scratch it and used a thin and hard object, such as a pen made of metal or something and while keeping it sideways to press down on the frame and straighten it up a bit and voila, ISSUE SOLVED.
hope this helped other guys like me before swapping them out for new ones which afterwards this would still come back.
sorry for my spelling, i'm not native english and maybe could've done better but i have to go to bed now. CHEERS