Car Alarms: New batt, crazy horn, subaru impreza, own horn

Question
Just put a new battery in my Subaru Impreza.  Now the horn beeps all the time.  I took the fuse to the horn out and I still hear a clicking sound under the dash.  The light inside go dim and then get bright.  No idiot lights come that should not be on.  When I crank the car it will idle higher then it should (around 2,000 rpm) and then the horn stops.  It is almost like it has a short somewhere.  I have done all I know to do and after this I am going to get my .45 and put her down.  Help please!

Answer
Sorry, but more input is required to give you
a good answer for this issue.

I need the make & model of the alarm system
if you know it please. And the year of the Impreza.

Also, is it a siren and flashing parking lights,
and an LED flashing in the dash when the alarm
"goes off"?

or,

Is it the headlights flashing, a worded "security"
or "anti-theft" blinking light in the dash cluster,
and the car's own horn honking?

This info helps me determine what alarm system
(after market or OEM-factory) that you are dealing
with.

Let me know and I will see if I can help you.

ALARMTEK
CARALARMMAN.com