Static in LF speaker only at low RPMs

[Jonathan Monetti]

I am an electrical spaz.  I really have very little skill in troubleshooting
anything with flowing electrons, so I'll just ask, since archives & web
didn't help me much here: 
 
-My CGT has static in the left front speaker (only).  Radio on or off,
doesn't matter.  Comes on at idle, varies with engine speed, and dissipates
as engine approached 1500 RPM and is gone by about 2000 RPM.  
 
I would have thought that a bad ground would give me static in all speaker,
and all ground connections seem fine anyway, but 
but what do I know--I'm a spaz
 
Any insight into narrowing this down would be much appreciated--starting to
drive me a little batty.  
 
Thanks
JM
 
Jonathan Monetti
'02 A4q 1.8t
'87.5 Coupe GT