warning beep on uneven bumps

[RS2Lover]

Hello friends, I'm new in this fantastic forum.
I live in Italy and I'm an owner of Audi-Porsche RS2 and of Audi Coupe S2 ABY.

I have a problem with my RS2 because when I push the brake pedal with the engine turn on, the pedal is very hard and the (!) turn on and beep and the car doesn't brake immediately but after the pedal go down and the car brake enough normally but I have the impression that the pedal movement is longer than before that this problem appeared.
I have this problem only when engine is turn on, when engine is turn off I have no problem.
Tasks which could be the causes of this problem?

Thanks a lot!

Bye!