Gran Turismo's engine sounds (up to and including GT5: Prologue) are lack lustre at best quite frankly. I think by more clean and more comfortable you mean boring and sleep inducing... Its shocking the number of times I've fallen asleep whilst playing GT where I bet a large reason for it was the boring monotony of the engine sounds.
Now I hope GT5 will be a massive improvement in this regard, theres nothing more dissapointing to buy a muscle car etc... in game only for it to sound like another sewing machine/hair dryer. Forza is massively ahead in this regard and one of the first things I do when I buy a car in Forza 3 is to take it for a test drive, look around the interior (yes only front interior unfortunately but at least theres 400 of them), rev the engine and then floor it to bask in the lovely sound as the car takes off. I have never ever done that in GT? Why because the engine sounds suck arse.
I hope PD fix this, it doesn't matter if the handling is fantastic and the graphics are jaw dropping if they've still got the same engine sounds... Its no where near the defintive game (for me at least). Engine sounds shouldn't be underestimated.