Alex2.7T

2001 audi a6 2.7t
Often , when driving car and braking to a make a full stop, I can hear a sudden quick bump noise underneath car, also sometimes happens when descelarating and acelerating right back again at a red light at the time car is about to stop completely. I was wondering if this is something normal on these cars since I haven't had any serious issues with that, it ONLY happens in these circumstances and not always, sometimes can't even notice it if I dont pay attetion to it.
I have been with this car for 3 years.