The MTX75 is a 'low drag' design, that is quite large clearences between the the input & output shaft gears,this reduces the friction factor between the meshing gears.At idle and some 'coast' or low rev situations the gears tend to 'rattle' or rollover,not a grind.Best test,drive into a fast food or bank drive thru,put the stick in neutral,let up the clutch,lower your window,you may hear a rattle that stops when you depress the clutch.As I said its normal for this box and can also occur when you pull at a slow speed in a gear that may be too high.Terry
