Welcome to the forums,
Interesting question there... I am clueless... however, you want to make sure you don't have some item that is heavy rolling around back there! Or rear area sag meaning a damaged frame in the back... Once you have time to really look and inspect maybe you will learn why it began swaying! You might also want to use the search tool (see the top blue toolbar) and key in swaying... might find interesting threads to help you answer your question.
Congrats on your 'stream! Hope to see you on the road!
Mrs. NorCal Bambi (traveling in S Tardis)