Speaker Blown??? 03 Trail Blazer

Hi, I have an 03 Trailblazer and I think the right front speaker might be blown, but Im not sure.
 
Its the speaker on the dashboard, on the passengers side.  Its the speaker where the buzzer makes the noise when the car is first started or when you open the door and the key is in the ignition.  When it sounds its worse, the buzzing noise is far louder than normal and it seems to carry on longer than when its not acting up.
 
Also, when I have the radio on, it gets that boucneback sound from that one speaker.
 
Does anyone know how to tell if the speaker is actually blown, and what types of places can replace them?
 
Thanks!