Horn goes off when starting car on occasion

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

Well, I've been dealing with this on the urq occasionally ... and now the
'85 4kQ does the same thing.  When starting the car the horn will begin to
sound without pressing the button.  I usually shut off the ignition switch
and try again and it will stop.  The problem seems like it might be tied to
low battery voltage.  

Has anyone else experienced this?  Has anyone else actually tracked down the
problem?  If so, I'd appreciate hearing what you found!

TIA!
Steve Buchholz
San Jose, CA (USA)