Had a pro sport back box fitted. I aint happy with the noise it makes when ticking over/idling as it sounds as if the car is running lumpy/chugging. Had diagnostics done and al ok, revs are ticking over lower which is the norm I am told with a free flow back box etc. I am just wondering if 'lumpy/chugging' sound from the back box itself can be cured in anyway? I have contacted the fitter who said bring it back but its 60 miles away!! so any suggestions how I might be able to solve this?