If your grass is this one Briza maxima - Greater quaking grass - the growing conditions quoted for it are "well drained soil", so very unlikely to be found anywhere near a bog.

There are Quaking Bogs, where water is covered by a thick mat of mosses and other plants and the whole surface moves up and down if you walk on it. I have even seen small trees waving about as the medium they are growing in moves. That said a quaking bog would not be "rattling".

I have always assumed the same usage as having a "rattling good time" (Dictionary definition number 2. That said - not sure what is really good about a bog?

Quack!
GtD.