See also O.H.U.B. and underbob
The act of squatting down....underbobbing...the resulting orgasm creates more of a grunting sound due to the position of the scrunched up body/torso. most times, body cramps result during the buildup due again, to position....resulting in one, nice loud grunting, painful yet strangely stimulating orgasm.
again, watch yourself on the overspray.
see also F.O.G.S.
self explanatory. if you can't follow the directions, you shouldn't be jacking off. Go gruntsquat!