For years I've been a fan of the song from their second album, Ágætis byrjun. When I look for the English translation, everything is translated, except for the "chorus":

I'm back

Inside of you

It's so nice to be here

It's just a quick stop

I fly around in underwater

On hotel connected to Electrical Tables and feeds

tju tju

But what is tju? Google Translate just gives me the same word back. I assume it's a vocalisation, like "Ooooh", or maybe a "yeaaah", but it could be an Icelandic term, like "oi" is to some English speakers (Australia, Britain etc.)

Any clues?