Hey,
In my experience (almost two years of cupra tdi) it is a bit noisy in the cabin at speed due to wind noise which depending on my mood can be hardly noticable to a bit annoying at worst.
Its the tyre noise that got me initially when I first got it and was learning to live with it, it is fairly noisy at 20-30ish but is better at speed although still more noticable than your average car. I have found in my experience that yokohamma parada spec 2's
help this a fair bit but for me the trade off came in wet weather as I found them a bit slippy but amazing in the dry+they look good as well. I'm now back on uniroyal rainsport 2's which are noticebly more noisy at spead and at 20-30ish but they are alot better in wet and about the same in the dry.
Having said all this it depends on where you live as I drive on crappy roads where the surface is shagged and makes the cupra very noisy-theres a section of the A64 near me and it's awful!! When I drive on motorways and say city centres it's not so bad but alot of the roads round where I live can be rough and noisy and the cupra amplifies this compared to an avarage car that has bigger profile tyres+softer suspension.
Engine noise isnt too bad when cold and improves alot when warm and really isnt noticable as a diesel at 50+ and in my opinion actually sounds nice when you boot it-I never thought a diesel ever could!
Another point would be that you gotta take the rough with the smooth-no pun intended! No matter what sporty car you get it will be noisy compared to a normal car it's the trade off for getting a better handling car.
Personnally I do get tired of my car when I'm knackered and just feel like floating home in a big fat A8 or something but I never get that sick of it that it makes me want rid because it has planty of boot, handles well, looks good, can easily get 50+mpg on longer runs or motorway driving and is cheap to tax considering the performance.
So it's worth asking yourself more than once what your really want and what type of driving do you really do most of the time.