This tank slapping issue seems to be reported, at the moment, by two journos out of the considerable number that have ridden it. BMW have invited 300 to ride the bike over 5 weeks ( not sure if that includes dealers, probably does? ). It is a fact that at least two bikes had problems, not a large number in the scheme of things but potentially a damaging issue to the GS brand........?
Stiffer frame, longer swing arm, more stability claimed by electronic suspension........you have to suspect BMW will be working flat out to determine cause, they don't want a Suzuki TL1000 on their hands with the flagship bike!