At 04:20 PM 5/14/2010, David Clarkson wrote:
>Could this be related to the lights and speakers sharing a common
>ground at some point?

Absolutely.  You've nailed the problem, I bet.  Because the
headlights draw a lot of current they raise the voltage of the ground
point and you're getting alternator noise feeding back into the audio
system.  I bet the whine changes pitch when engine rpm changes.

Yours,
David
"Grounds are funny things" -- unsung gardener.