What could be causing my car to do this?

I have an 03 Chevy Trailblazer with a little over 100,000 miles on it. Every time i start my car i hear i grinding noise for about 5 seconds and then it disappears. Then when i start driving i hear it again but only at low rms. Also, when just before i come to a stop my brakes make almost a farting kind of noise and push back on my foot like its studdering. I know its not my brakes or rotors.