Doesn't change w/rpm or vehicle speed? That almost rules out engine/drive train mechanical. What electronic device would chirp at a steady rate? Cell phone low battery, vehicle alarm low battery, stray volts getting to the horn some how (maybe a loose horn relay ground wire?) Fancy radio?
Charging varies w/rpm but likes been said remove the fan belt and test.
I dunno....
You might have a pizzed off critter in your defrost duct
Good luck
Dave
