i had the 1.4 engine in 2 ax gt's, 2 zx's and a xsara, now these engines were 8 valve, some were carb and some were injected (single and multipoint). when you got to 4000 rpm the engine became quite noisey(Boomy ?), but a few revs before and after it went away. now i know your is 16 valve but do you get the same? dont forget, its a heavy car with a small engine and you have to work it a bit to get some go out of it