Bought my first Jeep used and it had some cheap after market alarm system. Used to always do weird things...beep by itself, or set off its own alarm for no reason. Sounds like a possibility for what you're experiencing
If that is an aftermarket siren maybe you can find the alarms "control box" and disconnect/uninstall it. Thats what i ended up doing and never had another problem
...he looks you crooked in the eye and he asks you if ya paid your dues, you just stare that big sucker right back in the eye, and you remember what ol' Jack Burton always says at a time like that: "Have ya paid your dues, Jack?" "Yessir, the check is in the mail."