This is probably the best BMW Z4 GT3 soundpack available here but, unfortunately, it's not without its faults.
Like others have said, volume and high-frequencies are too high in this soundpack, and it can become a little annoying.
Being so loud and harsh (compared to other cars in the game), means also that it drowns the other effects (such as tyre, road and curbs sound FX), which can influentiate how you "feel" the driving.
I'm not sure what you could do other than sync your files with steam and try to replace them again.
Try some of my other mods and see if they work on your system.
Otherwise I'm not sure what you could do, sorry