Took delivery of 'new to us' 20,000 mile MY17 a couple days ago. It's nigh on perfect and looks / feels like a brand new car. But I wanted to drive it well and check for any oddities.

At slower speeds, there's an occasional gargle sound. Not harsh but subtle and not constant. Just comes in and out. It's sounds more airy than watery. Doesn't sound like a liquid related issue - which is odd given I've said a gargling sound, I know. More like an airy gargle.

Anyone know what it could be?

Right,

I've identified this as being related to the brake / brake pedal... but the noise is high up behind the dash.

Why would certain pressure / speeds / use of the brake pedal make for a gurgle sound high up, behind the dash.