Check the transmission where the belt goes, it may be worn out and when it takes speed, the entire washing machine starts to shake, so when it washes and does not take so much speed, it does not make noise, move the pulley where the belt goes with your hand and if it has play, that is the problem, remember to unplug the washing machine, it can also be the bearings of the box or motor
https://www.youtube.com/watch?v=jwKKEJSViSs here you have a video exactly of the problem that I think you have, luck and tell us how it was
the washing machine that appears according to the model you are commenting on ..... has nothing to do with the previous one.
http://www.lg.com/ar/lavarropas/lg-F1200TD-carga-frontal