Automotive Forums

Hi All,
I am new to this site and as you can see, i need some help if figuring out my problem.  I have a 2003 Audi A6 2.7.  I bought it with 36,000 miles on it.  I have driven it on the highway for about 1200 miles so far.
Recently  i hear this rattling noise coming from the front end of the car, underneath and it is only there when the engine is running.  When i switch the engine off the noise stops.  The rattling is there when i am not moving and parked with the engine running.  Any help on what this can be?
Also, secondly, when i am in traffic and i have the brake pedal lightly pressed i hear a scraping noise and a knock in between also.  This does not happen when the bake is firmly pressed.  
Both these problems usually start after i have been driving the car for a little bit.  
Please let me know anything that might help me figure the issue out.  I have the car still under the dealer warrenty for another 2 months and would like to get it fixed before that.
Thanks
Sami