Hoping someone knows whats up since my problem isn't exactly what others experience.

Car horn works
The doors successfully lock with the key fob.
The car successfully arms when using the keyfob, I know because I've tested it by opening the door and the alarm goes off.

I use to be able to put in into and take it out of silent mode but now that doesn't seem to work. When I hold the unlock and lock buttons together (as instructed in the service manual) the lights flash as expected but the horn doesn't honk to indicate the alarm is no longer in silent mode.

Any ideas?