It is Windows that is producing the sound. On Vista it is Control Panel -> Sound -> Sounds -> "Default Beep". On XP it is Control Panel -> Sounds and Audio Devices -> Sounds -> "Default Beep".
Edit : You said "devices". On a device it is Settings > Personal -> Sounds and Notifications -> Events (warnings, system events)
I had noticed that as well and was curious. So there's no way within Basic4PPC to disable the beep for that particular scenario then? Not like it's a big thing, it just sort of makes you think there's an error everytime.
It is Windows that is producing the sound. On Vista it is Control Panel -> Sound -> Sounds -> "Default Beep". On XP it is Control Panel -> Sounds and Audio Devices -> Sounds -> "Default Beep".