Speak Up, Mr. Bose

[Kneale Brownson]

Our V8 #2 has a dead spot in the right front when I first turn on the radio--presumably the passenger front door speaker system not working.  After a moment, there may be a high-pitched wavering whistle followed by "normal" sounds from the speaker.  Intermittently, after 15-20 minutes of use, the same speaker gets sounding gravely--sounds like there's a stone bouncing on the cone.
   
  Is this a failing speaker amp or something in the radio itself?  Rest of the system currently seems to work OK.  Anything an electronic dummy can fix?  Any place I can send it for repairs?