I have this same rattle, check:
Battery cover.
Dipstick is in correctly
Oil level
It comes from the left side of the engine (as you look at the front of the car, but it tends to go away once warmed up)
From driving a C2 in the past, I'm used to a rattly engine.
Not solved this problem but I have a GT not a 133 but I'd be interested to hear some suggestions