In absolute terms the 787 is extremely quiet, the relative stuff is if your ears pick up noise from the gallley area. Though often mentioned here and elsewhere, it has never been a bother to me. 7A would be my preferred seat here, 7K is at risk of being deemed a crew seat, so I tend to avoid that one. If you're not so far off from departure it's unlikely that 7K will be taken off you, but if it's a long time away it's a bigger risk that they'll change it at some point.