Mine has a similar noise and I too noticed that the BTCC cars have it. Personally I'm not worried at all. It is just a symptom of being cossetted by modern cars, so hearing the REAL sounds from an engine and transmission can be rather alien to us, to the point where we wonder if the car is going wrong!
exactly that ^^^
so much is defined on a modern car by its refinement. Road noise, tyre noise, exhaust and engine noise are deleted as best possible from the cabin by the manufacturer to maintain a quiet cockpit and driving environment for the user
when you start to fettle with that balance, noises that were either to quiet to hear and have now been amplified by modification, or now enhanced to perform with a more aggressive nature with comfort no longer at the forefront then the noises will indeed sound alien.
if you took a standard car and stripped it of every item designed for comfort and sound deadening you would hear all manner of noises that would otherwise go totally undetected.
on a similar note, when you start to go really hardcore its not the noises that get you its the smells. ive owned some monsters in my time and the sensation of fear as the "is that petrol i can smell?" or the "that smells like burning oil!" moments happen are nerve racking to begin with.
just listen to your car, when things sound bad, they usually are as they have that shrink into your seat sound that you know is gunna cost hundreds. everything else is merely the car. that simple