Car Alarm: LED Flashes to beat of stereo

["Sam" <none@xxxxxxxx>]

I have a Black Widow 1800 Car Alarm installed in my Mazda3.  Everything
is stock inside the car. I noticed the other night  while sitting in the
car and listening to the stereo that the LED was flashing to the beat of
the stereo. The heavier the beat, the stronger the flash.  I only had
the ignition in the ACC position.  This problem is not always easy to
replicate; however, it shows up most of the time.

The car installer said that he's never heard of this problem before.
Any thoughts?

Thanks
Sam