That code usually means the car can't talk to the siren, which is usually because the battery inside it is dead. OEM ones are well over £100 I believe, and blind riveted into place. Cheapy aftermarket ones might work.
Mine used to go off as well, but no siren, just flashing hazards. I'm sure I disabled it somehow, but can't remember how
I think I might have turned it off with the long coding helper in VCDS, it was years ago.
Also make sure no bugs are flying around inside the car triggering the ultrasonics. That's happened to me a few times as well