From today come an alarm sound (buzzer located on rear fuse box)) every time when I pressed brake pedal. I was check brake level (OK, add to max), brake pads - OK (middle of life) and brake lamps bulbs - also OK. I do not know from which reason or part come this alert. Need help.

FL2 2011 2.2 diesel 110 kW

Did know there was a buzzer there, its not something thats been added like a towing electrics warning to say your trailer/caravan lights arent working, and its that which is faulty?

It will be a relay on its way out, it's not a buzzer,

Have factory tow bar, but disconnected and unplugged.
Also try spray - clean electrical connector with air gun.
It is real buzzer (3 cm piezzo speaker).

pictures? Former Mod/Member, with the most post & Chicken George Arch nemesis

If it is a speaker, then it looks like a speaker from a non-factory towbar (that sounds when the indicators flash to let you know the indicators are working).

If it's sounding when the brakes are applied, then you have a short circuit somewhere - I would guess?

Do you tow anything with your car?

If not - get the towbar (and electrics) completely removed rather than just unplugged.