Why do (music) radio stations play loud music over phone interviews?

I don’t know if this is a universal thing, but certainly BBC Radio 1 does it all the time: when interviewing somebody by phone, they play an intrusive hi-hat-heavy CHIKK-chikk-chikk-chikk-CHIKK-chikk-chikk-chikk instrumental track for the whole duration of the interview. They do the same with listener call-ins.

If you’re trying to listen somewhere with background noise, like on a car radio, all you can hear is the high-frequency music and it totally drowns out the voice you’re trying to listen to.

What is the purpose of this annoying habit? I assume there must be a reason, and it’s not just to annoy people?

My WAG is that it’s an audio watermark so the interview can’t be used elsewhere.

That makes sense, but does it have to be so loud?

I’ve heard similar things here in NYC. WCBS-AM is an all-news radio station, and occasionally they try to be very cute by playing a song in the background. If someone would measure it objectively, they very well might say that that music is NOT loud enough to drown out the newsreader. But it so damn distracting!!! (Especially since the song is often related to the news item only very tangentially, and my brain is trying to figure out the connection when it ought to be listening to the news.)