[s-cars] Front Bose Speaker Noise

[everett2487 at adelphia.net]

Hey guys,
The other day when I turned on my stock bose radio I noticed a loud noise coming from my fron drivers side door speaker.  This isn't just normal static it sounds like its getting a signal from something.  When I turn on some music the other speakers work fine and the wierd noise in the bad speaker is lessened and it plays the music somewhat but sounds staticy.  The noise seems to go away more as I turn up the volume.  
What could cause this? bad speaker? possibly a bad amp? Is there a separate amp for the front speakers since there is one for only the rear speakers? could it just be a bad ground somewhere?
Thanks in advance,
Chuck
'92 S4