If you're talking about the chirp that is separate from the horn, from my perspective as an American in the USA, that same chirp sound is common among many Japanese brands in this country.
There's a good chance if you hear that chirp from other Japanese brands, that your vehicle likely has it too. The default is it to be on, so I'm surprised your vehicle doesn't have it turned on.
In the US manual, this is what I found to deactivate it. The same steps can be done to re-activate it.
Page 2-26 of the 2016 Subaru Crosstrek owner's manual
Perform the following steps to deactivate the audible signal. You can also use the same steps to restore the function.
1. Sit in the driver’s seat and shut all doors and the rear gate.
2. Hold down the REAR (UNLOCK) side of the power door locking switch.
3. While holding down the REAR (UNLOCK) side of the power door locking switch, pull the key out and re-insert it into the ignition switch at least 6 times within 10 seconds after Step 2.
4. Open and close the driver’s door once within 10 seconds after Step 3.
5. The hazard warning flashers flash 3 times to indicate completion of the setting.
You may have the above settings done by
your SUBARU dealer. Also, for models
with a multi function display, the setting
can be changed using the display. For
details, refer to “Keyless buzzer volume
This is for North American specification vehicles, so I am unsure if these steps will work for your region.