Ford C-MAX - shes sounding like a go kart - chewbacawaka

Hiya guys n gals I have a 2011 1.6 cdti cmax I bought around a month ago shes been running fine however she has recently developed quite a concerning noise which I can only relate to as a petrol go kart. When revved in neutral shes sweet as a nut but when giving it some throttle when driving she makes noise theres no noticable loss of power n drives fine just this noise any ideas or help would be appreciated? cheers oh shes done 39k if that makes any difference.

Ford C-MAX - shes sounding like a go kart - Peter D

You may have an exhaust leak. Get it checked. Regards Peter

Ford C-MAX - shes sounding like a go kart - chewbacawaka
This was my first thought but would have thought it would do it when revving in neutral if thiswas the case?
Ford C-MAX - shes sounding like a go kart - Peter.N.

Its not producing nearly as much exhaust pressure in neutral as it is under load.

Ford C-MAX - shes sounding like a go kart - Railroad.

You may also have an exhaust baffle broken away inside causing resonance, whether or not it's blowing.